What is the difference between Ubuntu and its derivatives?

The main two differences between Ubuntu and its derivatives are the backing and the default installed packages. For all official derivatives, you can convert between variants by installing certain packages.

Here is a small list:

Ubuntu

Ubuntu comes with the Unity desktop environment. The underlying Unity platform is still GNOME, but instead of using the GNOME Shell interface, Unity uses the Unity shell.

Ubuntu and Unity are commercially backed and supported by Canonical.

To convert an installation into regular Ubuntu, install ubuntu-desktop .

Kubuntu

This is the KDE flavor of the typical Ubuntu (which is GNOME driven). The primary difference is that Kubuntu comes with KDE as the default Desktop Environment, as opposed to GNOME with the Unity shell.

Kubuntu is sponsored by Blue Systems. Canonical stopped backing it in 2012, but it is still an officially recognized Ubuntu variant, which means that it gets build machines, test machines, CD image distribution servers, etc. dedicated to it.

To convert an installation into Kubuntu, install kubuntu-desktop .

Ubuntu GNOME

Ubuntu GNOME aims to have a mostly pure GNOME desktop installed by default.

Ubuntu GNOME is community-driven. It was originally called Ubuntu GNOME Remix; it was renamed to Ubuntu GNOME when it became officially recognized. Ubuntu GNOME is very new: its first release as an official derivative was 13.04 Raring Ringtail, which as of 6/9/13 is the current release.

To convert an installation into Ubuntu GNOME, install ubuntu-gnome-desktop .

Xubuntu

This is a lighter weight, highly efficient and optimized flavor of Ubuntu designed to run on older computers. It uses Xfce which is a proven faster Desktop Environment than both KDE and GNOME. This is a typically simpler slim interface.

Xubuntu is community-driven and operates under a Strategy Document. It is also officially recognized by Canonical (see Kubuntu for what that means).

To convert an installation into Xubuntu, install xubuntu-desktop .

Ubuntu Server

Ubuntu Server is optimized for use as a server. It does not come with X.Org, and as such does not use any graphical environment like a desktop environment or a window manager. Instead, it comes only with a CLI environment.

Ubuntu Server is commercially backed and supported by Canonical.

Mythbuntu

The counterpart to Xubuntu - Mythbuntu is designed to be an entertainment powerhouse. Focused around being a Media Center it includes many drivers and setups for TV Tuners, TV Out cards, and has a Media Center application (MythTV) integrated into the Desktop Environment to facilitate the entertainment powerhouse it advertises.

Mythbuntu is an officially recognized Ubuntu variant.

To convert an installation into Mythbuntu, install mythbuntu-desktop .

Lubuntu

Lubuntu takes the aims of Xubuntu and pushes the Desktop Environment to an even more bare bones lightweight variant:

• LXDE (Lightweight X11 Desktop Environment) in releases up to 18.04, and
• LXQt in releases after that. Both are very efficient (LXDE used GTK2, it was being ported to GTK3 where it was deemed to heavy, so the devs ported it to Qt5, they then joined the Razor-Qt team forming the newer LXQt project). It's a more efficient (the lightest official flavor out of the box), power saving, fast, lightweight Desktop Manager than XFCE (though if using GTK3 apps some of its lightness will be lost).

Lubuntu is community-driven. It is officially recognized as a variant by Canonical.

To convert an installation into Lubuntu, install lubuntu-desktop

My Opinion

I've used the first three before and I believe all have some backing from Canonical (or other corporate backing) while Lubuntu is still relatively new and community driven. Though if you have a very old/slow computer it certainly might be what you're looking for.

Figured I'd add the other flavors of Ubuntu I knew where out there

In addition to the above listed there is also:

Edubuntu

This flavor is designed with Educational intent. Runs very close to the vanilla Ubuntu release though it comes with many additional applications that are best suited for an Educational environment. It also is configured and stylized with kids in mind.

Edubuntu is an officially recognized variant.

Ubuntu Studio

This flavor is geared towards those who deal with multimedia (Video, Audio, Graphics, Design) on a daily basis. Comes bundled with many applications, codecs, and drivers required to facilitate those activities.

Ubuntu Studio is an officially recognized variant.

Ubuntu CE

Ubuntu CE (Ubuntu Christian Edition) is Ubuntu designed for Christians who wish to maintain an "Christianly" lifestyle. This comes bundled with a lot of religious software and security tools to help protect moral religious obligations.

Ubuntu CE is an unofficial derivative.

Nubuntu

This project is idle, but it's intent was to bring stronger hardened security to the stock Ubuntu installation. It targets security practitioners like penetration testers.

Nubuntu is an unofficial derivative.

Fluxbuntu

Fluxbuntu does not come with a desktop environment like GNOME or KDE. Instead, it only comes with a window manager called Fluxbox.

Fluxbuntu is community-driven. It is an unofficial variant.

Currently there are 10 Official Ubuntu flavors:

Ubuntu

The most common and known, Ubuntu uses the Unity Desktop as default and creates an standard desktop environment for TVs, smartphones and desktops. Ubuntu is not considered a lightweight distro although it works on some low end hardware.

Download - http://www.ubuntu.com/download/desktop
Information - https://askubuntu.com/a/521700/7035

Kubuntu

Most Windows users love this one since the transition from Windows to the KDE desktop is very easy to grip. To top it off, KDE is known to give pretty much many customization options for the user, ranging from general ones to very specific ones. This is also considered something bad (not from me at least) because it gives you a LOT of options to customize. Don't be amazed if you find an option for your fridge there. Like Ubuntu, Kubuntu is not a lightweight distro.

Download - http://www.kubuntu.org/getkubuntu
Information - https://askubuntu.com/a/521701/7035

Lubuntu

It is one of the lightweight alternatives to Ubuntu. Easy to learn and recommended for old hardware that you want to bring back to life.

Download - http://lubuntu.net/
Information - https://askubuntu.com/a/521702/7035

Xubuntu

Like Lubuntu, Xubuntu is a lightweight distribution. It offers several friendlier features than Lubuntu and it offers more customization.

Download - http://xubuntu.org/getxubuntu/
Information - https://askubuntu.com/a/521704/7035

Edubuntu

Focused on education. The installation procedure offers many prebuilt learning packages

Download - http://www.edubuntu.org/download
Information - https://askubuntu.com/a/521705/7035

Mythbuntu

Focused on offering a complete HTPC solution. From TV recording and similar activities to wathing a Movie or TV Series list.

Download - http://www.mythbuntu.org/download-type
Information - https://askubuntu.com/a/521708/7035

Ubuntu Studio

For avid multimedia users, it focuses on the Multimedia aspects of a system, It offers video/audio design & edition, Multimedia Authoring, 2D/3D Design, several preinstalled video editors, audio editors, graphic editors, digital design, raw image applications and any other multimedia editor needed for a full blowned multimedia workspace.

Download - https://ubuntustudio.org/download/
Information - https://askubuntu.com/a/521710/7035

Ubuntu GNOME

It offers users a sleek, fast and elegant desktop with many integrated features that work together to make the end user's life easier.

Download - http://ubuntugnome.org/download/
Information - https://askubuntu.com/a/521711/7035

Ubuntu Mate

It offers users a new desktop look using the Mate Desktop experience and mixing features and hardware requirements from lightweight distributions with more robust distributions. A reborned unique desktop experience.

Download - https://ubuntu-mate.org/
Information - https://askubuntu.com/a/585167/7035

Ubuntu Kylin

Developed primarily for China, Ubuntu Kylin offers many unique features not found in other flavors of Ubuntu (Apart from Mandarin as default ^^). It originated from the Kylin operating system designed in China by the National University of Defense Technology. The name Kylin comes from the Mythical Chimerical creature Qilin, which is a creature that when it appears it means a good omen (Prosperity or Peace). It is often called the Chinese Unicorn, which would be simply amazing when Utopic Unicorn arrives.

Download - http://www.ubuntu.com/download/ubuntu-kylin
Information - https://askubuntu.com/a/521713/7035

For Benchmark, CPU & Memory Usage, Minimum Hardware Requirements, Recommended Hardware Requirements and User Recommended Hardware Requirements, ISO Download Size, Look after installed and Desktop used please see the answers below for the respective Ubuntu Distribution.

All 10 distributions shown independently below offer the following:

• 10 Official Ubuntu Distributions (32-bit and 64-bit)
• Hardware Requirements (Minimum, Officially Recommended and My Recommendation)
• Unique Features
• Resource Usage & Performance
• All share similar Hard Drive I/O performance, Network Speed & Installation Time
• Apart from Edubuntu, Mythbuntu & Ubuntu Studio offering some unique installation options, all have similar installation procedures
• General GPU usage and performance actually varies more on what type of Video card, CPU, Amount of RAM and Motherboard you are using than on what Desktop you are using. In any case, at the end you can see the overall FPS performance for each Desktop.
• Test took one week and was done with the following Hardware:
  • CPU: Intel i7-4770
  • Intel Haswell Integrated GPU
  • Samsung SSD 840 Pro 256 GB
  • RAM: 4 GB DDR3
  • MOBO: Asus Z87 Pro
• SDD was formatted each time a new distribution was tested
• Office Apps means the following:
  • LibreOffice Writer, Calc & Impress opened with a simple document
  • For the Cases of Lubuntu & Xubuntu, the Office Suite was Gnumeric and Abiword
  • For the Cases of Mythbuntu & Ubuntu Studio, there were no Office Suite. Because of this, the Full Apps tests for them, does not include any Office Suite.
• HDD Usage means the hard drive space used after installation.
• Full Apps means the following:
  • Includes all applications from the Office Apps
  • Firefox opened with 20 Tabs showing the following sites: Ask Ubuntu, Ubuntu, Lubuntu, Edubuntu, Mythbuntu, Ubuntu Studio, Ubuntu Gnome, Ubuntu Kylin, Xubuntu, Lubuntu, Kubuntu, Ubuntu G+, Launchpad, Phoronix, Ubuntu Discourse, OMG Ubuntu, WEB UPD8, Slashdot, Linux Foundation, LibreOffice.
  • For the case of Mythbuntu which does not come with Firefox by default I used Chromium. I also had to exit the MythTV Application which launches by default to do the tests.
  • The Real Hardware Requirements are based on my personal opinion on how the user would perceive Ubuntu when using it. Will it be slow or fast. Will it load apps quick or take longer. Is the desktop responsive or sluggish. How much resources does the distribution actually take. This are my personal hardware requirements when trying out this particular distribution, but as they are personal, they can vary from hardware to hardware and user to user. The objective is to give the user an idea of what actual requirements could be needed and proceed from there on.
• The CPU and RAM usage is to give the end user an idea on how much that particular distribution uses when having several applications opened. This should be taken litely since the scenario could change. For example having Blender opened while rendering a video can use more CPU and RAM than having LibreOffice opened with several documents. So do not take this resource usage seriously, only use it as a basic guide, especially since the type of CPU and CPU power can dramatically change the usage value (Eg: Comparing an Intel P4 2.4Ghz with an Intel i7-4770).
• THe CPU and RAM usage is tested AFTER the process has finished loading. This means that the CPU might spike when loading an application but will then settle after the loading process has finished. The average value when settled is the one I take into account. Same goes for RAM.

Lubuntu

It is one of the lightweight alternatives to Ubuntu. Easy to learn and recommended for old hardware that you want to bring back to life.

• ISO Size - 730 MB (32-bit) / 740 MB (64-bit)
• Desktop - LXDE
• Download - http://lubuntu.net/
• Initial Desktop Look:

Lubuntu 32-bit

Hardware Requirements:

• Minimum Recommended

  • CPU: Pentium II (233+ MHz) + PAE Support
  • RAM: 384 MB
  • HDD: 2.5 GB
  • VGA: 16+ MB Video Capable of 1024x768
  • CD/DVD drive or a USB port for the installer media

• Officially Recommended

  • CPU: Pentium II (400+ MHz) + PAE Support
  • RAM: 512 MB
  • HDD: 3 GB
  • VGA: 32+ MB Video Capable of 1024x768
  • CD/DVD drive or a USB port for the installer media

• My Recommendation

  • CPU: 1.2+ GHz
  • RAM: 1 GB
  • HDD: 5 GB
  • VGA: 128+ MB Video Capable of 1024x768 & OpenGL 2.0+
  • CD/DVD drive or a USB port for the installer media

Benchmark Tests

• CPU Usage
  • 0 Apps - Less than 1%
  • Office Apps - Less than 1%
  • Full Apps - 2%
• RAM Usage
  • 0 Apps - 165 MB
  • Office Apps - 196 MB
  • Full Apps - 430 MB
• HDD Usage - 2.2 GB

Lubuntu 64-bit

Hardware Requirements:

• Minimum Recommended

  • CPU: 800+ Mhz 64-bit Processor
  • RAM: 256 MB
  • HDD: 2.5 GB
  • VGA: 16+ MB Video Capable of 1024x768
  • CD/DVD drive or a USB port for the installer media

• Officially Recommended

  • CPU: 800+ MHz 65-bit Processor
  • RAM: 512 MB
  • HDD: 3 GB
  • VGA: 32+ MB Video Capable of 1024x768
  • CD/DVD drive or a USB port for the installer media

• My Recommendation

  • CPU: 1.2+ GHz
  • RAM: 2 GB
  • HDD: 5 GB
  • VGA: 128+ MB Video Capable of 1024x768 & OpenGL 2.0+
  • CD/DVD drive or a USB port for the installer media

Benchmark Tests

• CPU Usage
  • 0 Apps - Less than 1%
  • Office Apps - Less than 1%
  • Full Apps - 2%
• RAM Usage
  • 0 Apps - 238 MB
  • Office Apps - 269 MB
  • Full Apps - 570 GB
• HDD Usage - 2.3 GB

Notes about Lubuntu

• The installation process is really fast.
• Booting was very fast. It got to a point where I did not know if I had actually rebooted or not because the monitor did not refresh that fast.
• Lubuntu is simple, fast and elegant. It uses a desktop with that Windows users will enjoy since it has the same look and feel as Windows XP.

Ubuntu Mate

It offers users a new desktop look using the Mate Desktop experience and mixing features and hardware requirements from lightweight distributions with more robust distributions. A reborned unique desktop experience.

• ISO Size - 1 GB (32-bit) / 1.1 GB (64-bit)
• Desktop - Mate
• Download - https://ubuntu-mate.org
• Initial Desktop Look:

Ubuntu Mate 32-bit

Hardware Requirements:

• Minimum Recommended

  • CPU: 750+ Mhz
  • RAM: 512 MB
  • HDD: 8 GB
  • VGA: 32+ MB Video Capable of 1024x768
  • CD/DVD drive or a USB port for the installer media

• Officially Recommended

  • CPU: 1.6+ GHz
  • RAM: 2 GB
  • HDD: 16 GB
  • VGA: 64+ MB Video Capable of 1366x768
  • CD/DVD drive or a USB port for the installer media

• My Recommendation

  • CPU: 2.0+ GHz
  • RAM: 2 GB
  • HDD: 20 GB
  • VGA: 256GB+ MB Video Capable of 1024x768 & OpenGL 2.0+
  • CD/DVD drive or a USB port for the installer media

Benchmark Tests

• CPU Usage
  • 0 Apps - 2%
  • Office Apps - 3%
  • Full Apps - 11%
• RAM Usage
  • 0 Apps - 145 MB
  • Office Apps - 240 MB
  • Full Apps - 445 MB
• HDD Usage - 3.1 GB

Ubuntu Mate 64-bit

Hardware Requirements:

• Minimum Recommended

  • CPU: 750+ Mhz
  • RAM: 512 MB
  • HDD: 8 GB
  • VGA: 32+ MB Video Capable of 1024x768
  • CD/DVD drive or a USB port for the installer media

• Officially Recommended

  • CPU: 1.6+ GHz
  • RAM: 2 GB
  • HDD: 16 GB
  • VGA: 64+ MB Video Capable of 1366x768
  • CD/DVD drive or a USB port for the installer media

• My Recommendation

  • CPU: 2.0+ GHz
  • RAM: 4 GB
  • HDD: 20 GB
  • VGA: 256GB+ MB Video Capable of 1024x768 & OpenGL 2.0+
  • CD/DVD drive or a USB port for the installer media

Benchmark Tests

• CPU Usage
  • 0 Apps - 2%
  • Office Apps - 3%
  • Full Apps - 10%
• RAM Usage
  • 0 Apps - 157 MB
  • Office Apps - 245 MB
  • Full Apps - 466 MB
• HDD Usage - 3.5 GB

Notes about Ubuntu Mate

• Feels like using Gnome 2 again but more slick and offers a nice style for it