The fresh GeMeCoD ANR Project has now a collaborative web site powered by dokuwiki. The use of Dokuwiki was suggested by Laurent Marciniszyn. Wiki software are very useful for collaborative projects. I have successfully used during the past three years the wiki software MoinMoin for the former EVOL ANR Project. I also tried by curiosity MediaWiki, which is far more rich and complex than dokuwiki or MoinMoin. Like MoinMoin, dokuwiki uses a text file backend instead of a relational database such as MySQL. Such a simple design suits perfectly the needs of small projects. Dokuwiki is written in PHP while MoinMoin is written in Python. There are numerous other free wikis available, see for instance the Wikipedia page on wiki software.
You may see the dokuwiki software in action by browsing the short introduction on the Fourier-Entropy-Influence conjecture of Friedgut and Kalai that I have created recently on the GeMeCoD wiki. The mathematics are rendered with the excellent MathJax.