Party with a Local - Party with a Local is a free app that connects travelers with locals that want to party.
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Milofy - Socialize with other like-minded couples
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Text Event Pics - Text a number to store and share photos together
Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.