Fossify Gallery on the official F-Droid repo
The removal isn’t directly related to the buyout/fork. Simple Gallery was taken off of F-Droid due to a dependency on the nonfree Google VR being discovered by IzzySoft¹ ². Fossify’s fork has removed the dependent features to be compliant³.
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Everything was forked and should eventually end up on F-Droid, but most things haven’t had a release yet. My understanding is that they’re hoping to do everything right immediately, including having proper new branding and all the shared functionality from Simple Thank You.
The F-Droid versions of SMT apps are perfectly safe and shouldn’t be going anywhere. (But if you have Google Play versions, I wouldn’t trust those anymore, those are owned by ZipoApps now.)
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They were, no new releases yet though except calendar