Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.

Apple App Analytics - Apple's very own iTunes Connect App Analytics

Eventbrite - Discover Great Events or Create Your Own & Sell Tickets

My Motiff - Allowing you to stay connected in realtime

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.

Usage Analytics in appFigures - Track usage for your app along side downloads, ranks & more