All the Migen wrappers themselves are licensed under the terms of the "CERN Open Hardware Licence Version 2 - Permissive" license.
The wrapped core themselves are under their own license. Always recheck the specific submodules to be sure but here's a summary that should be accurate (for the gateware parts):
no2usb: "CERN Open Hardware Licence Version 2 - Permissive"no2muacm: "CERN Open Hardware Licence Version 2 - Permissive"
Any small utilities / scripts / misc things in this repository which is not gateware is licensed under the terms of the MIT license.
Refer to the header of each file to see which license it is under.
See the doc/ subdirectory for the full text of those licenses.