We use a number of external library on ZeroFps so we don't have to code everything on our own. The basic rule is if there is something we need and no one feels like coding on it we use a library if we can find a good one. Here is a list of the libs we use and what we use them for.
Graphic: For graphic we use OpenGl (1.5+) and Glut. To handle the loading of all opengl extensions we use Glew.
Sound / Music: Sound is handled with OpenAl/Alut and music by Vorbis.
Script: For scripting we use Lua and our own custom lib LuaW to handle to creation of the Lua glue functions.
Physics: Physics is handled by Ode.
Platform: SDL is used for the basic platform independence and we use SDL_Image to load images.
Other: TinyXml is our way of loading XML files.