Couchsurfing

Since  I'm in Berlin, this has been one of the main source of free activities. Random people creates activities free to join, based on their own interests.
Activities like: frisbee playing, volleyball, soccer, pub crawls, Spati crawls, movies, BBQ, visit to abandoned places, ....


Fully reccommended to people who likes to do stuff but does not know people in Berlin yet.
Feel free to create your own activities too.
More Information:  http://www.couchsurfing.org/search/activity/in/current