@ctrlaltdog@chitter.xyz ahh
i can't really suggest many oss replacements for it, because i definitely still use keep--but if i had to exclusively use oss, i'd probably go with emacs org-mode since it covers everything keep does, with the exception of it's interface and syncing meaningfully with mobile (there are apps, but not many are that great)
it does let you export and lot of other formats though
@ctrlaltdog@chitter.xyz as for hosting, i mentioned that git wasn't a notes app, but it would be a pretty decent way to sync it in a way others can collaborate with you, since org is all in plaintext!
you basically only need ssh access to a server you own, or a github/gitlab account
mobile support for git isn't super-great, but i do use it to sync my keepass database between my computers and my mobile stuff