Whenever - Casual calendar app for iOS
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Avenue - Event messaging app for WWDC attendees
pretix - pretix helps you to sell tickets for your event in an easy way. It supports multi-lingual events and provides a wide range of features
Loxi - Easily add an events calendar to any website.
Ticket Tribe - Sell tickets online with no fees per ticket