From the website:
SLIGE is a Win32 (i.e. Windows 95 or NT or 3.1 with Win32s) program (compilable also for DOS and Linux) that produces brand-new levels for DOOM or DOOM II. If you're tired of the levels and PWADs that you have, you can use SLIGE to generate dozens or hundreds or thousands more. Some of them will probably be pretty good, too (he said modestly).
Use of Procedural Content Generation Methods
SLIGE generates random levels which can be loaded into the above games.