Jellow is available as part of OPEN DESIGN Initiative. The Open Design initiative is very much like the Open Source initiative whereby Jelllow's initiative is made available free to use as well as for further development.

Jellow Basic which is the core of all Jellow products will always remain free to use and all products of Jellow are licensed under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

You can read the details here:
http://creativecommons.org/licenses/by-nc-sa/4.0/
and here:
https://creativecommons.org/licenses/