The Cooperative Software License (CSL) is a copy-far-left (as opposed to copyleft) license that aims to rectify some of the issues that arise when using a copyleft license such as the GPL, namely, that your work can still be used in some extent by commercial entities and other for-profit ventures. It is based on the Peer Production License, and is adapted to be more applicable to software.
Licenses like the CSL and any Creative Commons Non-Commercial License are not libre (free as in freedom) software licenses, as they restrict the freedoms of certain user groups and use cases. This is why the CSL is classed as a copy-far-left (as opposed to copyleft) license. It is therefore incompatible with (and thus cannot link to) software released under licenses such as the GPLv3 or the MPLv2. It's important to keep this in mind when using the CSL for your project. The CSL is, however, compatible with less restrictive open source licenses, such as the MIT License or Creative Commons 0. The Free Software Foundation lists reasons why the Peer Production License (the basis of the CSL) is not a free as in libre license.
I am not the author of the CSL. These pages are entirely unofficial. The CSL was created by raddle.me user jadedctrl. The official source for the CSL can be found here. This site simply exists to mirror its content, and to provided a formatted version of it.