Indigo Bananas 2
Works ok but it's not perfect - often misses discounting some items if the collection is somewhat large (20+ items) and has to be paused, undone, deleted and redone. There were a fair number of items not on sale, but the collection that was set to be on sale was running in %Discount.
The default sale countdown messages can be edited to be more coherent (and should be because they are a bit ungrammatical). But the issue with inconsistently applying discounts to all items in a collection is a big negative for me.
It is faster than similar apps in applying/undoing discounts. Needs work, but I'd use it in the future if it gets improved some.