Introduced in 1990, the Apple Extended Keyboard II, M3501 replaced the Extended Keyboard. Changes include some cosmetics, a slightly softer and quieter key click, and an adjustable height bar. Featuring an ADB port on both sides for cable connection to the Mac from one and a mouse in the other. As with it's predecessor, the Extended Keyboard, it includes guide posts for templates that came with many software applications. Apple's last mechanical keyboard, it is still one of the most popular keyboards ever with it's clicky Alps key switches!
Keyboard comes with an ADB cable and matching mouse. Note that this keyboard came out before the Apple Desktop Bus Mouse II, so depending on your Macintosh Model, it would have been used with either mouse - Apple ADB Mouse or ADB Mouse II - take your pick.
Keyboards available as Nice, Light, Medium and Severe discoloration, and priced accordingly.
The template guide shown in the last picture is for illustration in case you're wondering why the pattern of discoloration appears the same on many of these keyboards. It is the only one I have been able to locate and it has been modified by the previous owner, so is not included.