Ocean Game. Geometry Games. There are interactive courses, tons of online tutorials, and one of my personal favorite ways to practice coding:

Here you can find 15 sample sets, each containing 28 questions. Those under 21 are allowed until 9pm. S Holiday Paint.

Vim is a highly configurable text editor used by programmers. The instructions are easy to understand and they cover basic learning that can be neglected with other "too busy" games.