There are following commands in OMGPI:

Name and Usage Aliases Permission Description
Player commands
/gameshop /shop Open game shop.
/hotbareditor /hotbaredit, /hbe Open Hotbar Editor.
/join /play Join currently running game (if game allows that)
/options - Open options menu.
/kit <name> /requestkit, /rk Select a kit.
/team <name> /requestteam, /rt, /teams Select a team.
/spectate /spec Leave game and spectate instead.
/vote <name or number> /v Vote for a map.
Management commands
/debug - omgpi.manage Show some info useful to developers.
/setgame [jarname] /setg, /gset, /gameset Select a jar to run. No arguments or random set game to random.
/setmap <name> /smap, /maps, /map, /mapset Select a map and stop voting.
/setkit <player> <name> /skit, /skits, /skittles Select player's kit.
/setteam <player> <name> /steam, /teamset Set player's current team.
/setrequestedteam <player> <name> /setreqteam, /teamrequestset Select player's team.
/settime <seconds> /timeset, /sett, /tset Set time left till game end.
/setupmode /sm Set game mode to setupmode, freezing all the timers.
/skipdiscovery /sd, /skips Skip discovery mode (time to discover the map) and start playing.
/startgame /start, /st Start the game.
/stopgame /gamestop, /sg, /gs Stop the game.