ZeeCal
ZeeCal is an iOS application (available for Android as well) I upgraded for a client in 2013. The app is simple - you create and share events with friends, colleagues, etc, and the app will keep you updated on any changes. The main idea of the product is that email calendars don't do justice to events; you might have them tracked on your email, but don't get the necessary alerts when event details change. ZeeCal makes it very simple by sending all notifications straight to your device including messages from users and event updates.
I completed the refresh of the app (version 2.1) in July of 2013.
I completed the refresh of the app (version 2.1) in July of 2013.