I currently use fruux (which is proprietary) to synchronise my to-do lists and calendars. However, I was wondering if there was a FOSS CalDAV service which I could use for free.
I have already looked into Nextcloud, and I don't believe it is what I'm looking for. I also don't want to use ProtonCalendar or Tutanota Calendar, as they only work with their own respective apps.
In a nutshell, I would like a service that:
Supports CalDAV
Is free (as in free beer)
Supports both calendars and to-do lists
EDIT: I am able to self-host some apps using Render, but they must be compatible.
Oh ok you should probably clarify that in the OP since everyone is giving you recommendations of self hosted software. It's usually assumed that's what someone's after when they are asking for a FOSS service.
There are some places that have one click (prepackaged ) Nextcloud installations. I set up one on Vultr in just a few minutes. If you’re savvy enough to even know that you want FOSS, which I applaud heartily, then you can handle a Nextcloud installation.