An abstract input state object that gets fed user events and updates itself based on a set of key bindings.
Basic particle system.
The Scene system is basically for transitioning between completely different states that have entirely different game loops and but which all share a state. It operates as a stack, with new scenes getting pushed to the stack (while the old ones stay in memory unchanged). Apparently this is basically a push-down automata.
An efficient way of drawing images composed out of tiles from a spritesheet, such as oldschool RPG maps.