PLIB is a set of libraries to write games and other realtime interactive applications that are 100% portable across a wide range of hardware and operating systems. It's used by Majik3D, FlightGear, and others, and includes libraries for GUI widgets, sound replay, geometry, scene graph, joystick, and fonts/text.
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.
geo-* is a set of tools for geocaching, including tools for accessing the www.geocaching.com, opencaching.com, opencaching.us, and navicache.com websites, tools for geocoding addresses and creating maps, and tools for manipulating Mapopolis place guide data. The focus of these tools is to provide a command line driven environment.
wad2svg takes a level file for the computer game Doom, and draws a 2D map of the level as an SVG (Scalable Vector Graphic) file. This can then be edited and/or converted to a raster image using a suitable vector graphics programs. wad2svg can also draw the node tree of a Doom level, and is designed to be extended to draw other aspects of the level.