frdoid is an alternative to google play that only provides open source apps

amber is an "isolated signer" which keeps your key and all it does is accept requests to sign things and has a set of permissions controls about what things it will automatically sign, or it pops up and asks you to consent

amber helps you protect your keys from being compromised by a bug in amethyst or other apps... and it also makes it safer to experiment with new apps that do other things, like "pokey", which vitor is always talking about lately, a nostr app that specialises in notifying you of events that you might be interested, like DMs or replies or reactions