Edit: I seek a server-less solution.

The only thing I can see is Linwood Flow but it looks like it's a really, really long way off before becoming a primary calendar app.

If it could just store all calendar content in 1 local file, then that could be so easily auto-synced across devices with !syncthing@programming.dev. Does anyone have any leads?

Hmm, I just now learned about Fruux, in this Reddit post...