An example to illustrate

Sésamath the current Math teaching network: http://www.sesamath.net/
Created in 2001, Sésamath is a recognized public interest and non-profit association.
Its goal is to favor :

• the use of computers in the teaching of Math ;
• cooperative work an co-training of teachers ;
• the services of support in the students' learnings.

Registered in a process of public service, Sésamath is committed to the values ??of free software. In 2007 and among 68 projects from 51 countries, Sésamath got the 3rd price from the UNESCO for its use of NTIC.
Sésamath distributes free and collaborative textbooks and notebooks for all levels of high school.
On their website dedicated to these works, everyone can download them for free and adapt if they wish.

From the start, Sésamath chose to use free licenses

• the GNU FdL (to give a real access to its works' source codes and allow their alteration/modifying)
• the CC-BY-SA (to insure virality: pour assurer la viralité: the preservation of works withion commons)

Thanks to this voluntarily very open choice, Sésamath was able to capitalize on the individual contributions of the network's members, to produce more elaborate contents (we shall speak about grade 2 of wealth to - see below) which could then be financially valued. This valuation has allowed the association to perpetuate its activity without losing the first sense of its action: proposing one space of cooperation and skills' mutualization between Math teachers.
On the contrary, a French teachers' network tried the Sésamath experience but failed because from the start, the chosen (or the unchosen) licenses did not allow them to develop their collective productions.