This looks very similar to Ropuka's Idle Island on Steam.

Not just being a "desktop idler" and the island itself, but also the "colored book tabs" interface, the way that you customize the island itself, even the "sketch with arrows" design of the customization slots (all visible on Ropuka's steam page screenshots).

Perhaps it's purely superficial; I haven't tried the demo so I can't really say for sure. (I personally found Ropuka overly simplistic, and I dislike the desktop idler format) But the similarities felt enough to be worth commenting on.