I was special projects chair at one guild. One year we did an ostrich round robin. an ostrich doesn't fly so you keep and work on your own quilt. everyone starts with a block or something for the center ( a ufo works good for this) and then every month I would draw two options out of a jar for the next round ie. add a new color, or use triangles. each month the quilter chose one option and added a border to her quilt. I think we had five rounds. at the end all participants had their names put in a drawing for a gift basket. I think this works best when there are two options and flexibility. Not everyone would want to add embellishments for example.
we also would have fat quarter lotto. pick a color or theme each month and everyone who brings a fat quarter is put in a drawing to win a bunch of them. we usually had two winners each getting 8 to 12 fat quarters.