Through the looking glass: Galden said he hoped to sell the device for around $20 or pack it in as a value item alongside a sports title. Unfortunately, neither of those scenarios materialized as the Secret Screen never made it into production... or did it?

The Nintendo 64 is arguably the last great cartridge-based home console. For many, it came during their formative years and for enthusiasts, has provided a wealth of historical information over the years. But even some of the most diehard fans may not be familiar with the little-known gem that retro gamer and preservationist Shane Battye recently shared.

The device in question, an accessory for the N64's controller that adds a second screen, was featured as a prototype in an issue of Electronic Gaming Monthly (September 1997) under the headline, "N64 Secret Screen Exposed." According to the article, it was conceived by Dane Galden as a way to prevent his brother from cheating at football games by spying on his play selection.

The accessory would have plugged into the 8-bit bus on the N64 controller, giving the player a private, second screen to make selections that couldn't be seen by others.

Here's where the tale gets particularly interesting. If you notice in the EGM screenshot, the story shares the page with an excerpt about Sega's upcoming console (the Dreamcast). That system, should you recall, featured the Visual Memory Unit (VMU), a memory card with a build-in monochrome LCD that, among other things, added second screen functionality.

It is Galden's belief that Sega executives saw the EGM write-up about the Dreamcast alongside the report about the Secret Screen, took that idea and used it to create the VMU. That's just one person's opinion, of course, but as Battye notes, the patent information does seem to corroborate this theory.

It's a fascinating look at a piece of history that never made it to market and perhaps even more importantly, a cautionary tale about keeping intellectual property under wraps. Ideally, Galden should have waited until the patents were in place before going public with his idea and kept all showings of his creation behind NDAs until then. Going public with the idea was just asking for it to be ripped off.