Think you know every product Apple has released? Think again. Here are five of the most obscure but interesting releases from Apple's long product history.

Over its 37 years in business, Apple has designed and marketed thousands of different products big and small, from support brackets to world-class computer systems. So it's not surprising that, over time, some of them have fallen under history's radar, making knowledge of their existence rare even among Apple history buffs.

We're about to take a look at five such Apple hardware products that are not only rare but also mostly forgotten. A few of them are hardly documented on the internet, and all of them represent interesting (if little-known) chapters of Apple's history.

Of course, none of these items are truly forgotten (otherwise you wouldn't find them on this list), but information on them is generally scarce. If you've ever used any of the following products, you have a chance to contribute to Apple history yourself by sharing your memories in the comments.

Apple Cluster Controller

Apple Cluster Controller (1983)

Thirty years after its introduction, the Apple Cluster Controller remains one of the rarest and most exotic pieces of commercial hardware Apple has ever produced. It served as a gateway between Apple computers (specifically the Lisa at the time) and IBM mainframe systems. One model of the Cluster Controller allowed up to seven Apple computers to connect to an IBM 3270 network, which required an intelligent protocol conversion process. As such, the Cluster Controller contained its own CPU and was a miniature computer unto itself, but technical specifications of this elusive unit are hard to track down.

Apple also released another ultra-rare product with a similar purpose in 1985: the AppleLine Protocol Converter, which allowed a single Lisa, Mac, or Apple II to connect to an IBM 3270 network. It is every bit as rare as the Cluster Controller.

Both are so rare that, at present, it is doubtful that any Apple collector on the Internet has either item in their possession. The only mention you’ll find of them is in old Lisa and Mac marketing literature and vintage magazine articles. Even a manual is hard to come by (so if you have one, let us know).

Apple Presentation System

Apple Presentation System (1994)

The Apple Presentation System provided a video converter box created by Focus Enhancements called the LTV Portable Pro that allowed Mac users to mirror video output to a TV set for presentation purposes. It also shipped with all necessary cables to hook it up and an introductory multimedia CD-ROM. Most of these were likely sold to schools, where they would have been useful in the classroom.

AppleColor Monitor 100

AppleColor Monitor 100 (1984)

Although users of the Apple II could use an ordinary TV set as a display (an early selling point of the machine), the picture from such a connection was fuzzy and full of interference. So many Apple II owners relied on the more direct composite video connection to a dedicated monitor that eliminated much of that fuzziness.

But it still wasn’t the ultimate in Apple II video. For the special class of user that demanded absolute sharpness clarity in a color display, Apple sold the AppleColor Monitor 100 and a matching RGB video card for the Apple IIe. Both items were very expensive in the 1980s, did not sell well, and are thus exceedingly rare today.

The AppleColor Monitor 100 presented a sharp image because it allowed a RGB video connection that separated out individual components of the video signal onto different wires so they would not electronically interfere with each other when combined, as is the case with a composite video connection.

It also included a very novel feature: a motorized angle adjustment. With the push of a button, users could tilt the monitor up or down inside its frame. No Apple brand monitor before or since has contained a motorized display, although the similar-looking Apple Monitor II allowed users to adjust the screen’s tilt manually.