I'm building an async community software called Booklet [1], and I use it to organize a couple NY-based IRL communities - including an indie founders group and a tech dinners series. It doesn't send calendar invites (yet!), but I find that the async format keeps members engaged over time. Plus, it's independent of social networks and communicates via email.

When I lived in SF, I used Meetup to start + run OpenLate, a tech meetup with a few thousand members. Not having access to member email addresses was the worst part of Meetup, and it's probably the main reason the site still has users. (Data portability is a big focus of Booklet).

[1] https://news.ycombinator.com/item?id=37585869