Well, in Mario Kart 8 communities are basically big lobbies where you establish a ruleset for everyone to race by, and then give the community code to whoever you want to join. The GAF OT has several communities for various rulesets like 150cc and 200cc. Also, there's a leaderboard system that gives you points based on how well you do in each race.
Based on what I've seen of Sm4sh tourneys, brackets aside it all looks pretty similar. Lobby codes, points for leaderboards, established rulesets, all that is there.