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.
My Xperia z3c from 2014 would be perfectly fine to use right now if Google didn’t absolutely bloat the crap out of their products and it had an easily replaceable battery. If companies would just support their products for longer or release the sources when it’s out of support i probably would have skipped several phone upgrades. But that’s probably exactly why they don’t.
I was just thinking about my moto x play still working. Shame about updates