I could never get mxCalendar to work. I'm not seeing update activity on it. I have a few clients who would switch their sites to MODX save for one thing: the Calendar/Events feature.
Both use Time.ly's event plugin for WP.
Good to know what a team of 15 people can do, and it shows. I never have ANY issues with their awesome events calendar.
I love to think that MODX can do just as well as they have. I'm not a coder, but I know MODX makes my life a heckuva lot easier. Maybe the solution is MIGX, maybe it's a port of time.ly's work (licensed of course).
I see all kinds of potential for a working MODX Calendar. One client I have uses a company's poor calendar website that often cannot process the URL correctly. He books events using it. I can see hooking foxycart or simplecart up to that.
We're all time-driven, right? Why not have an awesome calendar add-on.