Before used copies of Rez made it on eBay and way before it was released on the Dreamcast the game went under the code name K Project. The K Project has always been a futuristic on rails shooter, but it went through a huge evolution to become the synaesthesia experience that the final game ended up being. This video below is an early demonstration of the on rails shooting gameplay with a person instead of the flying wireframe avatar in the final release.
Check below for more videos of K Project and see the progression of Rez.
This video has an artistic style similar to Rez, but the game is vastly different from the final version. Notice the meter in the middle of the screen and how bright lights flash when an enemy is shot down.
Now we’re getting closer to Rez. The more developed version of Project K has sounds that play when other ships are shot down, a similar HUD and a layout this is similar to the first level of Rez. The major difference is that you play as a ship rather than a hacker.