From Quake Wiki
QuakeC is a language developed by id Software for their smash hit game, Quake. It is inspired by the C programming language, but has many many differences. While not particularly powerful, it made Quake one of the most easy to edit games of its day and spawned literally millions of mods. In fact the total quantity of mods easily exceeds Quake 2, Quake 3, and Half-Life combined.Template:Citation needed
QuakeC is compiled with a QCC compiler (such as FrikQCC or FTEQCC) into a progs.dat file. The file is read by the virtual machine inside the engine. This method is secure and cross-platform, much like Java.