SkillMint - Find, meet and rate people with common skills and interests. Community-driven rating system.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
ACTIVE JumpForward - JumpForward serves over 150,000 users and 175 college athletic departments with recruiting and camp management software built to keep you compliant.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Guestboard - Lead powerfully-organized group events with Guestboard – a modular event platform that gives groups of 10-1000+ people a central space to coordinate, build excitement, and save money. No more crazy email threads. No more massive group texts.
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.