Yeah, it's a mod you download and install. It's pretty easy as for as mods go too. The only difficult part I had was with styling it, but that's because I wanted it to fit a little side block on our portal, not the default wide version.
You can see it in action on our portal here,
but it also expands to a wide full page version by clicking the title link. Note that you don't need to have a portal, you can just use the full page version or place it under your board index or something.
This is where I got it.
This is where I got help styling (skinning) it. But again, this is not necessary if you're using the default version and default forum styles.
You can see this post of mine if you want the side block prosilver chat_body I made.