Take a simple folk or hymn melody and harmonize it (4 part chorale style) at least 8 different ways. Voice leading should be logical, though occasional voice crossing may be permitted. You are not bound to stay in any particular tonal area. The challenge is to give the listener a good sense of “flow,” despite what may be rather unconventional harmonies.
Extra credit: score the results for chamber orchestra as a “theme and variations” piece.