Deadlock is a small, lightweight MUD based around dueling wizard wars. It is an experimental project which has the aim of exploring the use of Scheme as a worldbuilding language and also building a small standalone library, netezu, suitable for implementing lightweight, multithreaded, server/client software on Unix and Win32 systems.
DeuTex is a wad composer for Doom, Heretic, Hexen and Strife. It can be used to extract the lumps of a wad and save them as individual files. Conversely, it can also build a wad from separate files. When extracting a lump to a file, it does not just copy the raw data, it converts it to an appropriate format (such as PPM for graphics, .au for samples, etc.). When it reads files for inclusion in pwads, it does the necessary reciprocal conversions. In addition, DeuTex has functions such as merging wads, etc.
D1X is a modification of the Descent 1 source that was released by Parallax. It's mostly compatible with Descent 1 v1.5, both in multiplayer (new features/fixes may not work with standard Descent, but d1x will still work fine using the old methods) and on the local machine. D1x combines code from both D1DJGPP and ldescent (which are both now defunct/assimilated into d1x) and adds many features of its own. D1x runs on Linux (SDL, SDLGL, GGI, svgalib, and GLX), DOS, and Windows (WGL, DirectX, and Direct3D (incomplete)). In software mode, optimized renderers are available for Pentium and PPro/P2 computers, and OpenGL hardware acceleration is also available.