Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
GoLocalBot. The project is closed - Platform for volunteers, NGOs, activists and crowdmapping.
Event Hunt - Startups and Tech Events Curated By Locals
Golden Volunteer Organizer - Automated volunteer recruitment, management, and tracking
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
DEED - On-demand app that makes volunteering easy, social and fun!