There is this very creative UT2004 mode that I used to play – ludocraft.oulu.fi/airbuccaneers/. Players basically pilot around hot air balloons and try to shoot each other with cannons.
The community seems to have died a bit, but I put up a server at 140.247.62.101:8777 , and will leave it up for as long as necessary to get people back! Please comment here if you want to play the game.