Yesterday I mentioned wanting Todoist's apps, but with self-hosted (or Canadian-hosted) storage.
Seriously. Todoist's app is great, but I can't find anything similar that lets you store your data outside the US. TaskPal is close; their data is stored in the EU except for file attachments (US now, EU soon).
I've got S3-compatible storage, MySQL, Postgres, and CalDAV handy, but nothing good to use with them. I need iOS, Mac, and Linux apps.
2DO (https://www.2doapp.com/) looks like a good choice for CalDAV on iOS and Mac, but CalDAV's got a long list of caveats: https://www.2doapp.com/kb/article/which-sync-method-should-i-use.html