JBoss (pronounced Jay Boss) is an
open source,
Java based application server. Because it is Java based, JBoss can be used on any operating system that supports Java. It is open source, but a company (also named JBoss) creates it. The company has a tech consultation service, but the consultants spend half of their time programming.
The Sims Online uses this to run its multiplayer games.
JBoss website (
http://www.JBoss.org)