@ajroach42 um... does https://www.unrealworld.fi/ count?
It's been in development since 1992, and, well, um... it's a roguelike, and it's very Finnish (: So "fun to play" may be one of those things like "dysentry" and Oregon trail (:
It is not, however, open source. But I think, if you're not familiar with it, that it may fit what you were thinking of...
@mjd My only real requirement is an open content license.
A closed source game is okay if the binaries can explicitly be freely redistributed, but I'd prefer something that allows modification.