MillionBalls is a web-based simulator meant to improve your real-life game. This is targeted beginner-intermediate level players who want to learn to visualize shots better.
Unlike typical pool simulators this one constrains you to the views you see as a player at a pool table rather than overhead or other unrealistic views. You'll receive immediate feedback about your aim and historical performance.
A thought: I suppose Virtual Pool is a pretty popular game/simulation in the billiards circles. Maybe you can get insights for keyboard/mouse interaction and graphical interface.
I remember playing Virtual Pool and I really liked the way they designed the interactions with the game.
You actually can impart spin right now with an undocumented feature. Use WASD to move the bridge hand and/or IJKL to move the grip hand. You can even play jump shots by elevating the bridge hand a lot and increasing the speed with +. The UI does get very awkward though, so all that needs work.
Ball-rail interactions need some tuning though. Things generally work, but they don't feel right to the experienced eye, so I don't want to set up more elaborate scenarios yet.
It will be very cool to be able to play through scenarios and figure out the most reliable route etc. .