Fallout 2
A turn-based RPG developed by interplay.
Now available on Steam, as well as GoG.com (http://www.gog.com/en/gamecard/fallout) and you can also buy the entire trilogy directly from Interplay [1].
A handy directory of almost(?) all the mods available for fallout 2 is available at No Mutants Allowed: http://www.nma-fallout.com/forum/dload.php?action=category&cat_id=15
the Fallout 2 Restoration Project is strongly recommended- it includes many mods that make the game more accessible (easily set the resolution for example) while only adding content that was originally planned to be included by the devs but were cut for time/budget reasons.