This is an Arduino port of the Atmel LWM network stack. Most of the code is taken as-is, with some small tweaks to make it work with the Arduino stack.
Original code from atmel can be downloaded here: http://www.atmel.com/tools/lightweight_mesh.aspx
The upstream branch contains only sources directly taken from the upstream zipfile, using the import script in this repository. The only modifications made are done using that import script.
The master branch contains the same sources, with additions to make them compile in the Arduino environment. The pinoccio branch contains some modifications specific to the pinocc.io software stack.
The code from Atmel is licensed under a custom open source license, as found in license.txt (but not without restrictions, so be sure to really look at the licensing terms). This is the same license as presented during the download process.
Note that comments in the source files indicate another, shorter and slightly different license ("asf license"), but also refer to license.txt so the exact terms are not entirely clear. When asked, Atmel replied on 2014-03-04 that the license.txt is binding. In version 1.2.1 (after my question), they added a reference to license.txt in all source file headers, but did not remove the "superseded" asf license, which makes things still slightly confusing.
(Me) In particular, there is a file called "license.txt", which contains a "LIMITED LICENSE AGREEMENT" that grants fairly liberal rights to the Software. However, looking inside the actual source files, I see that most of them contain a header with a different and slightly more libraral license (referred to as "asf_license", which I take to mean Atmel Software Framework?).
(Me) Could you clarify what the intent here is? In particular, I'd assume that the license in the header of a file applies to the content of that file, and needs to be retained when reusing or redistributing (parts of) that file. However, does the longer license in license.txt also apply and do I need to keep that one distributed as well?
(Atmel) The license.txt file supersedes the asf_license (Atmel Software Framework License).
(Me) However, does the longer license in license.txt also apply and do I need to keep that one distributed as well?
(Atmel) Yes, license.txt should be distributed.
The import script is licensed under a more liberal license, see the file itself for details.