Atari-joysticks were the most common type of joystick used in home computers back in the 1980s and 1990s.
The name derives from the Atari 2600, which first featured this type of joystick.
In the purest form, an atari stick is digital and has five switches; one for each direction + fire button, and a 9-pin connector.
All computers were compatible with this basic kind of stick, but almost all had extra features in their joystick ports such as extra fire buttons or analog inputs.
The connector's pinout goes like this:
9-pin female sub-d connector:
1 - Forward
2 - Back
3 - Left
4 - Right
5 - not connected
6 - Fire
7 - +5V
8 - Ground
9 - not connected (or 2nd fire button)
It's quite easy to build your own Atari controller. Just buy five switches, some cable and a 9-pin connector. The signals are activated by tying them to ground, so just connect ground to one pin of each switch, and one direction to the other. Then arrange the switches on a piece of board or a box so that they make sense (up goes up etc) and hey presto!