By far the biggest and most consistent and engrossing rouge-like game around.
`Free' but not open source - the author wants people, for example, to discover how to beat the Arch Grand Lich and not just lookup up in big_lich.c that he's vunerable to having big rocks dropped on him.
Rumoured to become open source at version 1.0.0 when the author intends to start work on a enhanced shareware version.
http://www.adom.de is from where the adventure begins...