Snaptivity - Real-time photo sharing with the world nearby

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

Flashgap - Time-delayed photo-sharing app of last night's embarrassment

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

WiFi Map - A crowdsourced list of routers and passwords

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.