Wotc's Companion app is not that great. Figured there had to be another way. Both links below point to the current v9.5.8.
Intended to be used in my playgroup. Hardwired player slots and simpler recovery-code model.
Best for broader use. Player names are entered in a textarea and assigned to letters automatically.
About: This is a work in progress, but everything should be working. Everything is saved via IndexedDB but there's also the recovery code, which should allow you to save everything in the tournament. Player, pairings and results.