Hey there @fishtail - thanks for your post!

Calendly integrates with the following calendar platforms:
Google
Office 365 or Outlook.com
iCloud
Exchange

There is not a Caldav integration at this time. I know this isn't exactly what you wanted to hear but do hope the information helps, at least somewhat!

is caldev integration on the road map?  do you know how many people out there use caldev??

Hello again! I cannot say that an integration on our end with Caldev is on the road map currently. I’m sorry! I also cannot speak to how many people are using Caldev. If you are interested in more information about Caldev I suggest reaching out to their support team as well. In the meantime, please consider the calendars we do integrate with. 

If you need your Calendly meetings to show up on your Caldev calendar, you can integrate with one of our current options - Google for example - then share your Google calendar with your Caldev calendar. I hope this helps!