In 2005 / 2006 SIMS Co. Ltd were working on a prototype for the Playstation 3, to use as their tech demo for future projects on the console. This demo was created with Unreal Engine 3, showing some buildings and an open world, but without any real gameplay planned yet.
The Virtual Boy was released in July 1995 in Japan and August 1995 in USA. It was met with a lukewarm reception that was unaffected by continued price drops. Nintendo discontinued it the following year. Due to the short lifespan of the system, only 22 games were released. Of them, 19 games were released in the Japanese market, while only 14 were released in North America. [Info from Wikipedia]
Celine found some images from early Virtual Boy Tech Demos / Target Renders in Super Power magazine issue #34. Most of them look like early visualization of released Virtual Boy games, such as Golf and Mario Clash. We can also notice the “Sample Demo” that came with the VUE Debugger software, in which you can move a ball around a three-dimensional field.
Also, Grooveraider preserved some videos of the demos shown at the Winter CES 1995 in his Youtube Channel!
Cyber Knights was a prototype created to develope a new 3D engine for the Playstation 3. It’s currently unknown if this proto was going to be a full game that was later cancelled or if it was just a tech demo.