If your purchasing xF is based upon calendaring, make very sure that that mod will do what you want. What it does, it does well. What it doesn't do, it probably won't do. The author doesn't want it to be a calendar, but only for events. If that works for you, great. Just be sure ahead of time.
I have some special things and the calendar of vB never was a real calendar, nor does XenAtendo fit my/our needs. I will finish the concept and probably will collect further ideas here. I assume a good calendar is highly neede by lot of people. Probably it would be a wise thing to share and test/develop together.
I am also in need of a good calendar with preferences for my private community site. I have many private events which I need to display and also auto post into a forum for people to discuss each event.
I need a calendar which will have
1. Recurring events (classes), each attached to some page. A user, who owns this page, should be able both edit a page and event (duration, frequency etc). Events can be overlapping.
2. Users should be able to add own "special" events
3. I wish to have several "layers" or calendars. So user can say show me "beginners only classes" and/or intermediate and/or advance classes.
4. it must be easy switch between month view / week view and day. Google calendar is very good but it is not integrated with XenForo.