Game looks amazing...

[Pull The Strinks!]

I was wondering if anybody knows what engine / tool they used to make this game?

[Cliff Excellent]

No idea about the engine, although one thing I can tell you is that basically all the art and music is public domain stuff.

[Ｈｅｎｋｅ３７]

It's node webkit.

[sketchylogicgames]

We used Construct 2. It's not very well suited to adventure games or visual novels, but it's great for rapidly implementing new features.