Impossu Puzzle is a hard combination puzzle, which can be played everywhere, even without internet connection.

There are fields with different dependencies and states. When you change one, another might too. Your goal is to get them all to be in the black state.

To make a riddle playable over time, and showable to friends, you can load and save them.
It's open source: https://github.com/AntonioNoack/ImpossuPuzzle, and downloadable by anyone.