These will probably be the last new ideas I post for a while. Hope you enjoy them:
A game where all magic is created by playing music. You have a flute that creates different magical effects depending on what note is playing as a drone in the background. Flutes in different keys would interact differently with the same drone. You can supply your own drone, but more powerful would be to use a drone that is already sounding in the background, like the electric hum of a generator, or the rushing sound of a waterfall. In a mechanical or steampunk world, droning sounds would be easy to find.
A game about visual hierarchy, where you can create, modify, and arrange graphic elements in order to achieve certain goals about the way a viewer would look at the composition. Different elements might draw attention more strongly, or hold attention longer, or direct the flow of attention in different ways. It could make a good puzzle game. People could play it to learn graphic design.
A game about software development, but abstracted, so you are building a system of interacting parts to accomplish some goal. You may add pieces to it, and you may factor out identical or similar components. These pieces would most likely be physical shapes that link together rather than actual code. You may also reorganize or refactor the system to make it possible to factor out more pieces. There is a tension between adding more, for short-term benefit, and refactoring, which is better in the long run.
A game where you can snake around as if controlling one end of Noby Noby Boy. But you also want to come back to your center, your foundation, so that you can move your center instead of just getting caught up in your head and hands. There is a tension there between continuing to snake around and collect stuff and deal with stuff, and taking the time to come back to your center and move from there, to reset.
A game where you are a small aquatic creature dwelling near the surface of a small pond, perhaps an artificial pond or pool in a garden.You spend your time close to the edges of the pond, as the open water in the center is more dangerous to you. The water is dark, but full not empty, and its depths are warm and reassuring. Sometimes it rains, rippling the surface and bringing colder water to the pond. It is always overcast. The surface colors are black and shiny gray, turning to orange and brown below and at the edges, the color of the soil and water. On land are the muted grays, browns, and greens of winter plants and stone.
Yay. Let me know if you have any thoughts to share about these ideas. :)