Angel is a 2D game prototyping engine based on OpenGL and C++. It was originally made by a group of employees at Electronic Arts Los Angeles for use in a GameJam they were planning for April of 2008. Angel provides many useful functions for prototyping gameplay, including simple physics, particles, text rendering, sound, input mappings, config files, pathfinding, and Python scripting.
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.
CADauno is a 3D modeling tool based on the NURBS surfaces. It aims to exploit the power of NURBS at representing free forms. It provides an interpolation facility ("skinning" technique), which enables the designer to create a closed surface passing through different section curves. This makes it possible, as an example, to build a human body 3D model starting from sections provided by a Computed Axial Tomography scanner.