Slim is available in C source form for Windows NT and generic UNIX. The C sources are program generated and not meant for human readers. The GCC C compiler is needed to compile Slim on UNIX. At one stage, djgpp could be used to compile it for DOS as well, but at the moment, djgpp hangs on a compiler error when presented with the Slim compiler.
To down-load the distribution click here.
The current (undocumented and somewhat obscure) sources used to develop Slim can be viewed by following this link.