What is the Oniken key in Desura?

I have Oniken in Desura from the Retro Groupee bundle. In the CD keys section, I can request another key for this game. The format of this key is: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX (x5).

Does someone know for what/which platform is this key? Oniken isn't released on steam (it's only in the greenlight section), and the desura key from groupees has the following format: XXXXX-XXXXX-XXXXX-XXXXX (x4).

Thanks for your help. :)