1. http://innovation.internews.org/blogs/opportunities-crowdsourcing-russia-and-ukraine
2. Amazon Mechanical Turk,
http://www.mturk.com/mturk/welcome
3. FixMyStreet Platform,
http://www.fixmystreet.com/
4. Ushahidi Platform,
http://www.ushahidi.com/products/ushahidi-platform
5. Adar, E., Huberman, B.A.: Free riding on Gnutella. Proc. First Monday 5(10) (2000)