Red/blue is Gameboy and looks a bit boring compared to Sapphire/Ruby. Yellow came out shortly after Red/Blue where you start with Pikachu.
They did it in a really good way though. Some of the pokemon are only available in one version so if you want to get 100% of the pokemon you need a friend with the other versions and trade with them. Very clever way to get people to buy a Gameboy out of peer pressure.
I did see on the freeroms website there was a Yu-Gi-Oh game.
