In the Overview section on a map, if you click the Game type attribute, the search results will be for maps with that tag.
Also, if you search for the tag in the standard search, most of the time, the result will return a match too.
@raspatan: I've come across some minor incompatibilities in Windows too, but they aren't too common. One example is Q3 Fortress crashing when toggling fullscreen in-game.
And of course, as for total conversions, it is Open Arena, World of Padman and Open Arena Mega Mod for me.
Edited 1.18 hours after the original posting.