A few years ago I took the Boom 2.02 source, and I ported it to use Open Watcom instead of DGJPP. I even went as far as getting it to compile for Windows.
Here's some of the stuff I remember doing with it:
For DOS removed Allegro.
Rewrote input code and tried unify keyboard and mouse inputs.
For DOS used audiolib from the Rise of the Triad source release for sound. (Even though the RoTT code release is GPL, I've always had my doubts about the audio library).
For Windows used SDL.
For Windows used a GLSL 1.2 shader for rendering (mostly used for scaling, but I also played with a 24bit color map).
Make files were reverse engineered from the Heretic and Hexen source release.
Removed a massive amount of comments, reformatted source files and moved functions/variables around.
Unfortunately due to inexperience the code repository is a complete mess. I can't even provide a detailed explanation of what's going on because I honestly have no idea anymore.
Over this year I've been putting together a retro PC as well as making some small contributes to Chocolate Doom, and in doing so I am reminded of this old code. Given that I have an environment where I can run and test a DOS/Windows 98 era source port, it seems like it'd be a loss not to continue with this.
Should I begin the process again from the Boom 2.02 source, using my existing code as a reference, or should I try and salvage it somehow?