A rotary encoder converts rotary switch movement to output pulses that can be interpreted by keyboard encoders.
Offered by Hagstrom, this unit is capable of operating as a stand alone device or may be used with a keyboard encoder. Its are suitable for driving direct inputs on a keyboard encoder to produce a keystroke or keystrokes for each change of position of the rotary switch.
Relevant Link: Hagstrom's Rotary5 Page
Rotary Joystick Interface
Relevant Link: Ultimarc's Rotary Page
Druin's Rotary Interface
Offered by Druin, this was one of the first rotary encoders for the BYOAC crowd. You can download the plans and build your own board. It can convert two 12-position mechanical rotaries, and it needs to be connected to a seperate keyboard encoder or gamepad encoder.
Relevant Link: Druin's web page