Where can I find a detailled description of all still included API, DirectX and OpenGL functions ? And where can I find a good reference, where most used functions are covered ? (or even all) I'm interested in writing a small c++ program which can update and manage the "api.def" of C-Lite.

Thanks for answering my questions.

All API functions covered are listed in api.def. Detailed descriptions of those functions should be easy to find on the Microsoft website, but you need to look yourself - lite-C doesn't include documentation about them.

For adding API functions, see:

http://manual.conitec.net/litec_api.htm
http://manual.conitec.net/litec_c.htm

For learning how to add a very complex API, like DirectX, it's best to have a look into the include\d3d9.h file.