seeking input - android apps for things - awful.systems

in the spirit of this post [https://awful.systems/post/625341], but from the other side I have a shitdroid that I can’t root because the vendor sucks, but google can go fuck themselves too. combined with that I haven’t androided much for about a decade and know nothing about the current ecosystem… I’m looking for good alternatives to a few things. free/foss preferred but I’m pragmatic over picky - if there’s a good paid option I’m willing to consider it immediate known requirements include contact sync, calendar (more business than personal but either works if it’s good). maybe also other things I should know about? judicuous preference to things that support open protocols and self-hosting (i.e. anything that has to use their service to operate - no go) tell me about good apps! I know about syncthing and photosync