Skyscanner - Skyscanner.com compares over 1000 airlines to find you the cheapest airfares, fast.
BeWelcome - Open your door to the world!
Kiwi.com - Find and book the best low-cost flights all around the world
Hospitality Club - Free network of people around the world who offer free accommodation, advice and help when they are traveling - hospitality exchange. Free membership.
App in the Air - The perfect companion for everyone taking a flight.
Trustroots - Travellers community for sharing, hosting and getting people together.