Interesting. Not released yet. There's a signup where you can get the source early (probably without an open-source license). Based on FreeRTOS. Nice to see a divergence from the usual shoehorning of Linux into stuff.
Thanks! I work at Mudita so I'll let you know more :) After singning up for the Developer Preview we will invite people in batches to the closed GitHub repo. We're still tinkering the docs and very actively developing the OS. When it comes to the license, we're aiming at GPL 3.