WEBook License
The goal of the WEBook's license is to do for textbook material what Free Software and Open Source licenses do for software: to use the commons-based peer production approach to generate a large amount of high-quality and free-content material, by accepting contributions, error fixes and comments from cooperating individuals, while safeguarding and properly acknowledging all these individuals' efforts. Contributors keep the full copyright on their contributions, but allow free use according to the prescriptions of this license.
The Creative Commons copyright license fulfills all these requirements, it is internationally accepted, reasonably concise and it has been scrutinized by legal professionals. A short version of the license is reproduced here:
You are free (i) to copy, distribute, display, and perform the work, (ii) to make derivative works, and (iii) to make commercial use of the work. You must observer the following conditions: (i) you give the original author credit for any reuse or distribution, (ii) you must make clear to others the license terms of this work, and (iii) any of these conditions can be waived if you get permission from the copyright holder. Your fair use and other rights are in no way affected by the above.
The full legal text is here.