Our guild ran a UFO challenge twice, two different ways.
First time - everyone who wished to participate made a list of up to five UFO's, stage they were in. Judges decided how many points a project (completed, which meant quilted, bound and labeled - if label was needed/wanted).
Quilters were divided into one of four teams. Each time you finished a project you brought it to the judges who marked down the progress and the points. You then show and telled your item. Team aggregate scores were posted monthly. At the end, all sorts of prizes were given out, some from quilt shops, some from guild, some donated by members etc. There were prizes for first one to bring in a finished project, first one to finish their list, one with the most points, team with the most points etc. Everyone agreed this was a really fun challenge, even without the prizes.
Second time - you listed up to five projects, as you finished you brought to show and tell and to judges. No points, a draw at the end for the first one to finish all their projects. This one did not go over as well partly because it was during our "Zoom" meeting phase (but not during Covid). Also, many of the quilters who participated the first time said they didn't have enough projects to complete to bother joining.
We haven't done one since and it's been a few years.