The choice of tournament directors!
Since 1988, SwissSys has been the choice of tournament directors who want to devote their energies to making events more enjoyable for the players -- not to wrestling with uncooperative software.
It makes pairings for Swiss system (and round robin) tournaments, following all USCF (or FIDE) rules for alternation of color, transposition of players--everything required to effortless and accurately run a chess tournament. It lets you print out pairings, standings, wall charts, upset results, new ratings, and lots more. In fact, there isn't much it can't do for Tournament Directors! It can import player registration information from the USCF supplement with just a few keystrokes. It is extremely flexible and customizable, making it the ideal assistant TD for all levels of competition. It has been used at major tournaments, including the US Open Chess Championship, World Open Chess Tournament and tens of thousands of other tournaments.