Take a look at http://www.appointmind.com/ http://www.appointmind.com/ SMS reminders are in the making and the rest is already available. I'm not sure, though,

Take a look at http://www.appointmind.com/ http://www.appointmind.com/ SMS reminders are in the making and the rest is already available. I'm not sure, though, what you mean by "Calendar invite".