> You can't 'selfhost' this stuff.

you can,

- kdeconnect can do clipboard & messages sync

- nextcloud (or anything else that does webdav & webcard) does calendar & contact sync

- Firefox (and chrome probably too) can sync browser history and share webpages feom one device to another

i'm not aware of anything that can remotely unlock another device, but that seems like a security risk to me (also quite hard to implement as pam is synchronous :/).

but you certainly don't need a closed ecosystem, building your own out of free components is very much possible.