Arrow keys to move, space bar to shoot, and a status line of enemy ships to clear. The original was written in BASIC by a twelve year old and printed in a magazine, and this is that game rather than a game inspired by it: the same ships, the same beams, the same abrupt end.
It runs about ten minutes and it is not going to surprise you. It is here because it is a clean look at what a whole game could be before anyone had decided what a whole game had to include, and because it is more fun than it has any business being.