The license for the project is GPLv3, with an Apache-style contributor agreement for Desura to use in their main releases. The Windows counterparts appear to be included in the open-sourcing as well. It's exciting to see where this will lead.
The reasons for the copyright agreement are explained by Protektor from Desura:
Everything was pulled as much as possible from how other Open Source projects do things.
We aren't trying to trick anyone or rip anyone off of their code. We just need certain things because we know situations are going to come up where we need the ability to do thing a bit differently because of how we do things.
For the Open Source version that is a given that they go into the contributors file, but seems like a major hassle for game devs to have to figure out who to include and who not to include based on what parts of the client they might want to use.
Additionally, the default build is stripped of Desura branding, as is done with many other trademarked and open-source projects.
Join #desura on freenode to chat with some of the developers and get involved. Anyone up for packaging? :)