TeamSnap - Sports Team, Club & League Management Software & Apps
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Spond - The easiest way to organize team sports or other type of group activities
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Simpler Sport - Save time managing your sports team
Bigtent - BigTent is a web-based organization and communication portal for groups.