I once played a game (Power Soccer) that used the Swiss tournament system to run competitions. Essentially, you played your entry and entered a lobby, and the tournament would start at a pre-set time. After you played your game, everyone returned to the lobby, and the next round was played straight away amongst players who had returned to the lobby (loads would quit after just 1 match!). After a few rounds using this system (essentially, you play people with similar records every round), a winner was determined. I thought it worked very well for an online tournament because quitters or incomplete/delayed games (games that were taking too long were terminated, declared a draw, and players returned to the lobby) had a low impact on the outcome compared to tournament brackets which would be impacted severely from quitters or no-results.