JRuby is very versatile when it comes to deploying, so there’s a number of ways you can try it right now!
The interactive tutorial at Try Ruby runs atop a sandboxed, server-side instance of JRuby.
Note that this version may lag behind official releases, but it gives you a general feel for what interactive JRuby is like.
JRuby’s interactive console, like many Java apps, can be started as a WebStart application.
You can download the console as a WebStart JNLP file or launch it directly on some browser by clicking below:
Some browsers also support embedding Java applets via the Java browser plugin. If you can launch the applet below, you’ll have a fully-interactive JRuby instance to play with.