A notable mention is https://ubports.com/en/ which is different from postmarketos in a sense that ubports uses old kernels with heavy patches. That means: good support for things, but difficult future.
PostmarketOS uses the newest kernels and tries to integrate their patches into mainline kernel, so that the reliability is maintained with all kernel developers.
GrapheneOS is an open-source Android fork lots of people like, it’s what I’m planning on using once I get a new phone
While I’m a fan of GrapheneOS, I think it could still be considered “tied to Google” both due to it being based on Android, and also because it only runs on Google Pixel phones. Graphene focuses more on security, then on privacy, but not so much on reducing our dependency on Google’s software and/or hardware.
Yeah those are things on my mind too, especially since Google moved Android behind closed doors.