Any 3D CAD programs for Ubuntu?

FreeCAD

If you haven't tried FreeCAD, you're missing out. It's a fully parametric 3-D modelling package that can be extended with Python. The interface is reasonably user-friendly, and feels like a "younger" version of Solidworks.

Installation: Just install freecad package , or newer version using PPA. Also you have an AppImage.

OpenSCAD

OpenSCAD is a software for creating solid 3D CAD models. It is free software and available for Linux/UNIX, Windows and Mac OS X. Unlike most free software for creating 3D models (such as Blender) it does not focus on the artistic aspects of 3D modelling but instead on the CAD aspects. Thus it might be the application you are looking for when you are planning to create 3D models of machine parts but pretty sure is not what you are looking for when you are more interested in creating computer-animated movies.

To install OpenSCAD, just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:

sudo add-apt-repository ppa:openscad/releases
sudo apt update
sudo apt install openscad

For more CAD apps see 8 Best CAD Apps for Linux

For 3D use Blender. I think it is the only real alternative. BUT you will have to do a lot of work, because it is focused on animation. Blender is extremely wide, you will have to find what you need, what is not always easy for beginners. For example, there are plugin tools to improve exact 3D modelling, you might customize views etc.

For 2D use DraftSight (not free software). It is a clon of AutoCAD, which means that you don't have to get familiar with new commands, workflow etc. For individuals it is free, Information about your behavior will be send regularly to DraftSight. Go to their Homepage and get the actual .deb file. DraftSight's disadvantage is, that there is no 3D.

BRL-CAD

Maybe BRL-CAD would suit:

BRL-CAD is a powerful cross-platform Open Source combinatorial Constructive Solid Geometry (CSG) solid modeling system that includes interactive 3D solid geometry editing, high-performance ray-tracing support for rendering and geometric analysis, network-distributed framebuffer support, image and signal-processing tools, path-tracing and photon mapping support for realistic image synthesis, a system performance analysis benchmark suite, an embedded scripting interface, and libraries for robust high-performance geometric representation and analysis.