How about an app akin to the Incredible Machine game [0] where you built Rube Goldberg-like contraptions, but for practical real-world projects, that lets you pick and plop components with a 3D interface and simulate the machine onscreen?
This thought just occurred to me that it could be a very entertaining and rewarding hobby.
[0] https://en.wikipedia.org/wiki/The_Incredible_Machine_(series)