If you have never played or even heared of Empire, than you haven't played any decent game yet!
Empire is a great multiplayer online war game. It's origin started somewhere in the early 1970's. See this detailed history
The empire community can be found in rec.games.empire
So how do you get started:
This is a client for the really, really desperate. If you are stuck behing a (company) firewall/proxy and can't affort to mis an update, you might be in luck if you can reach http://emproxy.tryba.nl/emproxy/. It's basically a webbrowser proxy to any empire server. The only thing you need is a browser that supports (session)cookies.
Since the default emproxy interface is quite horrible for intensive use, more sophisticated clients should communicate more efficient by RPC calls in HTTP. EmpRPC is a very simple example of the XMLRPC service at http://emproxy.tryba.nl/empire.servlets/servlet/XmlRpc. Show me more :)
Just like Drake Diedrich's empire-hub it's a program to enable co-rulers to to share a connection. Thus enabling them to be online at the same time. The mayor difference is that empire-hub is well tested and written in C, while my program is underdevelopment and written in Java (good news is that the source can be compiled with eg GCJ to create a standalone version that doesn't depend on a full JVM). See the download area for source and jars.