From Bulbapedia, the community-driven Pokémon encyclopedia.
Pokémon Zeo! was a website founded on October 13, 2000. It was created and maintained by The Echidna and Purity, formerly of Pokémon Aaah!. On it were resources with which fans could create fake Pokémon cards, as well as some Zeo fake/custom sets.
Its forums were once quite active, though not so much so in the Pokémon sections of them. Still, the Zeo News posted (almost) daily usually had to do with some Pokémon-related events.