Here are some of the commands that can do useful things for you:

stat fps-shows the FPS (Frames per second) ,useful for checking how well the game runs on your PC. in Ut2003 and UT2004 games, if it's below 40FPS, it'll show up in yellow,if less than 30FPS,it'll show in purple and if it's above 40FPS, it'll be green (everything's good basically)

enable cheats (only works in Ut2004 and possibly UT3)-in order to use cheats in certain modes of this game, type this command first then type in the required cheat.