If you want to recompile WarpIn, be aware that there are two different parts to the thing.
  1. The back-end is standard C++ code without any OS/2-specific code. This should therefore compile with every halfway decent C++ compiler on any platform. Jens has written this using EMX/GCC, Ulrich develops using IBM Visual Age C++ 3.0 (henceforth VAC++), so at least these two compilers do work.

  2. The front-end, written by Ulrich M”ller, contains lots of OS/2-specific code. warpin.cpp requires the OS/2 kernel, gui.cpp requires PM headers. I am aware that there is at least one VAC++-specific thing I'm using (_doserrno), so if you get this to work with something else, please let me know.
Makefiles. There is one monster makefile (/frontend/warpin.mak), which is for rebuilding the whole thing using NMAKE and VAC++. There are other makefiles which have been written by Jens or others (I don't know), which are probably for GNU make.