Compiling/Using a Linux source on Mac OS X

It all depends on how portable the developers made their program. Unix is not GNU/Linux and therefore not all programs will compile that easily on a Mac as they would on a typical Linux system. Expect developers to be lazy – some might even try to compile their code on Windows and Ubuntu only.

How to install NEAT C++

However, this one's relatively easy.

Download and install XCode if you haven't already (the OS X developer tools from the Mac App Store, by registering on Apple Connect or the disk included with your Mac if it's an older one)
Download the NEAT source code
Open up a Terminal, cd to the download directory
Enter make. Wait a bit. The software will compile now.
Run the binary with ./neat p2nv.ne (here, "p2nv" is just an example file provided).

How to install other applications

Other applications might need a configuration step before. Usually, the procedure is outlined in a file called README or INSTALL. Just follow the instructions there.

In most cases, compiling a program should be as easy as: