Around Gen 4 time, I remember coming across a Japanese (official) Pokémon browser game - most of what I remember was that you could chat with people, walk around different areas with a Gen-3/4-era overworld sprite, and I think you could download stuff like wallpapers?

I don't remember if there were any battles, but I think it might have been tied to Yahoo! Japan possibly, and there were tons of other people playing all at the same time.

Does anyone remember what it was called? I've been looking for the name for a while but it seems to be super obscure.