Rock'n 4 is an arcade game that was only released as a prototype in Japan. Details about its gameplay and developer are scarce, owing to its unreleased status.  It is highly likely that it was an early attempt to create a music-rhythm game, a genre not uncommon in Japanese arcades. Further information would depend on the unearthing of any surviving documentation from its development or testing phases. Its rarity and unfinished nature make it a highly sought-after item among arcade game collectors and enthusiasts of unreleased titles.

Rock'n 4 (Japan, prototype)

Rock Duck (prototype?)