Can Plugins Display a HUD/UI?

Hey, I'm new to minecraft plugin dev. I know there are limitations to what you can do with server side plugins, but I was watching my brother play on a server where they displayed some information heads-up-display on mining/fighting/etc. experience in a dark, semi-transparent box that faded in and out on the right hand side of the screen. He doesn't have any client-side mods installed so it must be server-side. Is there API for doing this? After searching the Bukkit API docs and the forums I have been unable to find anything—but mostly cause I don't know what I'm looking for. Thanks in advance!

 

The box on the right is a scoreboard

 

Yes like RainoBoy97 said. It's usuing the scoreboard

See the bukkit api docs at http://jd.bukkit.org/rb/apidocs/org/bukkit/scoreboard/Scoreboard.html