Schenkel system is a modification of the Swiss sytem. The Swiss system is commonly used when there are too many players to play a round-robin tournament.
The Page playoff system is a playoff format used primarily in softball and curling at the championship level. Teams are seeded using a round-robin tournament and the top four play a mix of a single-elimination and double-elimination tournament to determine the winner.
The system requires teams to be ranked in some way, as the top two teams have an advantage over the bottom two. This is usually accomplished through a round-robin tournament, which eliminates all but the top four teams.