Ten years ago the first Polymath project was launched (link to the original proposal of Timothy Gowers).
Polymath can be described as massively collaborative mathematics, i.e., a large groups of mathematicians works on a predefined problem and each member posts his or her (partial) ideas, so that the collective makes progress from each small step that everybody contributes (Wikipedia).
Up to now there were 16 projects (some of them are still running), and several of them were successfull (or made significant contribution to the solution of the problem). The results are published under the pseudonym D.H.J. Polymath. Here is the link to the general Polymath blog: link.