Chocolate Doom
Conservative Doom source port.
Freedoom
Crowdsourced Doom IWAD file.
Irmo
Client-server multiplayer gaming engine.
WADptr
Doom WAD file compressor.
SDL Sopwith
Port of the classic game Sopwith.
SMMU
Older Doom source port.
Lhasa
Free LHA implementation.
C Algorithms
Liberally-licensed C algorithms library.
Yoctolisp
Lisp interpreter written in a weekend.
Agito
Subversion to Git conversion tool.
Revol
Psion Revo Linux distribution.
JBMgen
Library generator for Archos GMini MP3 players.

Hackery

Sinclair QL disks
Reverse engineering some old floppy disks.
Password teacher
Program passwords into your muscle memory.
Automatic SLIGE megawad
A new 32-map Doom MegaWAD every day.
3dshot
DOS-based raycasting engine.
BSD License generator
Generate a license for your project.
Brainfuck.NET
Compiler for the Brainfuck programming language.
Self-modifying Brainfuck
Brainfuck language variant.
Tools...
Various tools and small programs.