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I am skeptical too, but the company is Finnish. Anybody know more about them? Edit: looks like a non-free OS indeed. The developer tools just seem to include an SDK. It's a pass for me.
For those curious, it's a continuation from where Nokia left with their Linux efforts, that's the roots in a nutshell. They did ship a smartphone with their own hardware in 2013. I still have it in my drawer. Definitely ambitious, and an achievement, for a small company tackle OS, hardware, dev experience, everything. https://en.wikipedia.org/wiki/Jolla_%28smartphone%29
Issues aside it was a beautifully designed device, you could see real innovation. Unfortunately Nokia killed it before it even shipped.