Originally founded by Australian-based Mewthree and Frogglet, the Pokémon Factory has been around since the mid-to-late 1990's (although none of the original staff members remain and the site has suffered more than one period of extended downtime.) Unlike the other sites in this Wiki, the Pokémon Factory was never intended to produce a playable Pokémon video game; back when it was founded, it was enough of a revolutionary concept that people could send in their ideas for new species and have those ideas made into finely crafted Pokédex screenshots. Even so, the pokémon PF puts out are of a high enough quality that it has earned a planned reference in Pokémon Treasures; PF was among the earliest sites to focus on fan-created innovations in Pokémon, and was undisputed master of that arena at least once in its long and varied history.
Although the Pokémon Factory is not currently pursuing its own playable video game, we do have a running forum RPG, the Pokémon Factory League, in which any pokémon approved for production by PF can be encountered (forum RPGs are Role-Playing Games in a broader sense and resemble multiplayer storytelling.) The PF League's current host, Bonzai, has ambitious plans for tie-in Flash games among other projects.
Further Info: PF's Light and Wind