A selection of alternatives to Google Play

1. F-Droid (https://f-droid.org/) – FOSS application catalog, I recommend.
2. AuroraOSS (https://auroraoss.com/#aurora-droid) is an alternative F-Droid client.
3. SkyDroid (https://skydroid.app/) is a decentralized application store.
4. Obtainium (https://github.com/ImranR98/Obtainium) – downloads applications directly from the source (GitLab, GitHub, F-Droid, SourceForge, etc.)
5. FossDroid (https://fossdroid.com/) – a new catalog of FOSS applications.

Bonus: Droid-ify (https://github.com/Iamlooker/Droid-ify), Foxy Droid (https://github.com/kitsunyan/foxy-droid) (2 more F-Droid clients).