Nyan cat is an internet meme, referring to an animated gif of a cat with the body of a cherry Pop-Tart flying through space, leaving a rainbow trail behind the cat; or to a video of the animated ?.GIF?, set to a remix of the song "Nyanyanyanyanyanyanya!", or to any of several Nyan Cat based games.
It's now on Amstrad CPC, with the music adapted by John McKlain and the code by Demoniak (just for fun !).
Beware the Amstrad CPC Nyan Cat video on Youtube isnt the last version available (current version is 3).
If you cant read the french forum, here is the same thread on CPCWiki's forum.