PokEdit is an online Pokemon Editor. It's like PokeGen, but you don't need to download anything, meaning you can edit your Pokemon in your browser.
Basically, any Pokemon editing system allows you to create/ edit Pokemon, edit items, change the Pokedex, change Mystery Gifts, loading/ saving files, etc.
PokeEdit Website
^ That's the link, but it currently just tells me "502 Bad Gateway".