Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
TripIt - TripIt is a travel app that creates a master itinerary to organize all of your plans for your vacation or work trip in one spot.
Event Hunt - Startups and Tech Events Curated By Locals
WorldMate - WorldMate is a travel app that helps individuals plan and organize trips. The app is available for Android and iOS mobile devices, and it is free to download and use.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Sygic Travel Maps - Itinerary planner for independent travelers