Johny.: @Yepoleb, I always appreciated our community involvement and work done around GOG. Did you get to implement game time tracking (this in particular is not SDK I think), achievements or other features in Comet?
Technically I'm not an expert on SDK, so I can't say much about reasons for it not being openly documented etc.
I presume for Steam it's different, since anyone should be able to publish a game there, so it was a priority for them.
Thanks! I only implemented authentication and achievements, after that I decided to work on the GUI to make the project more presentable and got demotivated because I still hate working on GUIs.