...It features its own programming language, and many users have contributed useful packages in various areas over the decades. It is GPL-licensed and largely written in Common Lisp. Executables can be downloaded for Windows, Mac, Linux, and Android; sourcecode is also available. An active community maintains and extends the system.
Website: https://maxima.sourceforge.io
Additional add-on packages for Maxima can be found at: https://github.com/maxima-project-on-github/maxima-packages
Plot 2D (plotting X vs Y) scatter plots directly to a compressed image file. Platform independent standalone package. Plot up to 12 series. ASCII options file. Console/Terminal and win32 GUI. Code is ANSI C with C++ encapsulation. Try it on the website.
Quake II Weapons Facotry (THE Team fortress for Quake II) meets Quake III Arena WFA. The engine is founded on Q2 GPL code, and uses the WFA media. Visit the main website for more details.