Found it!
Fountain will be available on zap.store once we add proper support for closed-source apps.
Discussion
This is great news. Fountain is a fantastic application and an even better use case and marketing tool for Nostr as a whole, showcasing how you can take your existing application and rip out your walled garden socials and integrate with Nostr, making your application that much more powerful.
I figured Orangepill App would have been the first to do this but kudos to Fountain