Just like the Legend of Zelda console game. Only better because there are fan made quests, tile sets, etc. Many of these fan created quests are bigger than full sized NES games. They have large overworld maps which include numerous locations containing multiple levels.
There is also a perfectly replicated clone of the original Zelda game. And there are non-Zelda mods as well. There is also a quest creator so you can create your own game. There is a large data base of graphic and sound material to use.
A new version, currently in public Beta is in the works.
Zelda Classics official home http://www.zeldaclassic.com/what.php
PureZC: the site I prefer for forum, quests and other ZC resources http://www.purezc.com/index.php
A turn based strategy game engine. There are perhaps a hundred fan created games to download. Many are World War II based. Including some fan created clones of various versions of the popular Axis and Allies boardgame. Other games range from ancient times to futuristic.
There are both single and multi-player modes. There are at least two active servers running at all times. There is PBEM support as well. The game is quite playable now, and has been for some time. But it is under constant development and refinement. A new unstable version (v1.3.1) has recently been released (May 13th, 2011) which added a new AI, drastically improved the existing AI, and has added a number of features that modders have requested.
Official site: http://triplea.sourceforge.net/mywiki
Download page: http://sourceforge.net/projects/triplea/files
Heres some info I posted on my Wikipedia user page: http://en.wikipedia.org/wiki/User:AWhiteElk/TripleA_%28computer_game%29
And heres a pictorial sampling of just a few of the games available: http://s22.photobucket.com/albums/b318/WhiteElk/TripleA