[zandorg]

I used to think 'Nethack' was multiplayer over the Internet - the 'Net' bit - but it doesn't appear it is. Is it?

[shabble]

No, there's limited interaction by means of 'bones' files if you play on the same host.

If you die and certain conditions are met, you'll leave your corpse, all your items, and a ghost for another lucky (or unlucky, given that whatever killed you will still be around) adventurer.

There do exist some multiplayer roguelikes, Mangband http://www.mangband.org/ is probably one of the most well-known/popular.