They have pushed a basic CalDAV (and CarDAV?) feature out on Migadu for what it's worth. I think they're new enough that they're considered beta and not in marketing materials.
Yep, if you contact them about it they'll provide you with more info. Both CardDAV and CalDAV will be available, documented and all, to the public in September/October. When I emailed them earlier today about it (pure coincidence) they gave me the necessary info on CardDAV and also directed me to a post[0] made by another beta tester explaining both DAV services in more detail.