Whenever - Casual calendar app for iOS
Calendify - Calendify is an event community where you can share, publish, and subscribe to event calendars. It helps you to stay informed about what you are interested in and what is yet to come.
Avenue - Event messaging app for WWDC attendees
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Loxi - Easily add an events calendar to any website.
Meetup for iOS and Android - Discover groups that are all about the things you love