Is it really somehow microsoft-related website? It seems like a phising website to me.
Why would they give away free motherboards?
Windowsondevices.com, registered under Microsoft, redirects to the dev.windows.com subdomain.
It's legit.
I don't think everyone who register will automatically receive the Galileo board.
There will be some vetting conducted, and I'm sure geographic distribution will be factored in as well.