"Stone Soup" refers to the Stone Soup folk story, where people contribute their supplies to make a great soup for everyone (it is developed by many people who contribute to the open-source project started by Linley Henzell as Linley's Dungeon Crawl).
Still a better name than NetHack (which is not a game about hacking networks... "Net" just refers to collaboration over net to improve the game Hack). There is also BrogueCE ("Brogue Community Edition").
I should probably have used the full names for clarity,
either way the acronyms mean, in order: Dungeon Crawl Stone Soup, Ancient Domains of Mystery and Cataclysm Dark Days Ahead.
ADoM = Ancient Domains of Mystery
Cataclysm DDA = Cataclysm Dark Days Ahead
I swear I didn't make the first one up ;) Edit: ah well, you got your answer already^^