Simple Mobile apps have been very popular among FOSS enthusiasts. I've personally been using the Gallery, Contacts and the Phone app since a few years now. It's a shame that it has come to this, will be on the lookout for their forks.
"we specialize in acquiring under-optimized apps in an industry that is highly fragmented. We use our optimizing operations, deploy its technology, and generate cash flow from the apps. "
"we developed an AI technology that knows how" "to monetize the right user at the right stage of their app experience"
(https://everything-pr.com/zipoapps-tech-talk-with-the-entrepreneur-co-founder-and-ceo-gal-avidor/)
Sounds like they just keep the apps around and try to squeeze as much money out of the users they have bought.