I made a post of a similar nature in the market forum: http://www.boonex.com/unity/forums/#topic/WANTED-Groups-Schedule-mod.htm

In that thread. I asked for a real groups calendar. There's no need to entirely reinvent the wheel on this one, because a pre-invented calendar app can be used as the base. I like the look and feel of this free one: http://www.luxsoft.eu/luxcal/index.php?cP=2

I want something like this so Group admins can post a schedule of activities, and so that each D7 Group can see more have it's own calendar. The same calendar could be used for a public schedule of activities.

Have a look at the Lux calendar, and see if the functionality meets your needs. If it does, make a post in the Market Forum thread I started. If enough interest in this is shown, someone might do an integration.