Looking for a Group Calendar.

Looking for Group Calendar that works with Wordpress, displaying a month view, that others can also update events on it as well.  Of course registered users or a different level that could access and update the calendar for their trip planning.  The purpose, besides normal upcoming events, is that a group of us that go camping together can put on the calendar our scheduled camping trips and we can plan them out in one location.  Getting everyone together to plan the trips with all the summer schedules on where are we going in 3 months and who else is going to be here or there.  Ideas, plugins, code?