That's not PO. That is another battle simulator named Showdown.
http://www.pokemonshowdown.com is the link.
Here are some differences:
- Does not require a download.
- Sprites move, moves are somewhat animated.
- Doesn't support unreleased Dream World Pokemon.
- Has Missingno., Random, Balanced Hackmons, and Hackmons.
- CCs have better movesets and items.
- One server.
- Has a better messaging system than PO.
I've been using it too, and I like it, beside the fact that unreleased Dream World Pokemon aren't supported.