You could probably use Homebox for this use case. It allows for locations to be configured, attach receipts/maintenance reminders/manuals, etc. Also has OIDC, invite links, and more. I use it to maintain my home inventory of stuff. I think you can also have separate inventories per person/group as well as shared ones within the same instance.
I’ve not used it myself but cal.com could work for you as well. Their docs provide instructions on how to self host.
ETA: I think I actually tried this out on the individual tier for my wife, she was thinking of doing some personal training / life coaching and using this to provide appointments. I thought it was flexible enough but didn’t give it an earnest try.
That makes much more sense! Figured it was inconsistent.
Missing the difference between 8 and 9?
Oof… that’s dumb. It seemed like decent software, wonder if anyone forked it prior to that
Edit: looks like there’s cal.diy on github. Not a fan of open source being a second class