ioquake3 (or ioq3 for short) builds upon id Software's Quake 3 source code release. It cleans it up, fixes bugs, and adds features. Its goal is to be the Quake 3 distribution upon which people base their games and projects. Its design goals include optimizing the engine for playing Quake 3: Arena, Team Arena, and all popular mods. This distribution of the engine has been ported to many new platforms. While it doesn't have PunkBuster (and never will), it does provide more security for servers and clients by way of various bugfixes which aren't in id's client.
RoseThorn is a cross-platform library for 2D and 3D games running on GNU/Linux (and possibly other Unix-like OSes) and Windows. Features include: hardware accelerated 2D and 3D rendering; Ogg and WAV Sound support with OpenAL; Lua scripting; BMP, JPEG, and PNG image loading and saving (from screenshots); easily created and modified user interfaces with XML and CSS, combined with Lua event handling; separate 2D and 3D libraries; support for multiple fonts in both TTF and bitmap formats; support for OBJ, 3DS, MD5, and RTM model formats; skeletal animation (a work in progress); support for UDP and TCP networking; thread and mutex support; a Simple Shader API; 2D animated sprites; and some basic cryptography support. There is simple event management, with key/mouse bindings easily customized from the in-game console, config file, command line, or GUI.