I wonder if you could implement a mod to work with Google Calendar? I haven't used it much, but it would seem to lessen the load of developing one. Don't know if there's an API or anything, just wondering out loud, eating some fruit loops
I dont think we need a "calendar". What we need is an event planning system.
Let people create a thread, with a date/time attached to it... and let people RSVP for it. A lot more simple. Of course, "Event Threads" need to be limited to specific event forums (similar to how you can create poll forums).
In a way, this is almost done. For an "Event Forum", just attach a date/time to the threads... and then you can use a the "like" system for the RSVPs.
It's quite astonishing what you thought you needed but actually never needed. My last forum solution was filled with bloat but looking back at it now I notice even more bloat and unneeded features that seemed to fill the gaps by developers wanting to include partial features instead of fully fledged needed features wanted by customers. Xenforo seems to fit this criteria in giving us what we actually need not what we think we need.