JavaScript is often a fairly good replacement. You can try it in your browser anyway, and you can do fairly impressive stuff with fairly little effort. It's pretty trivial to put together an HTML page that grabs JQuery off the AJAX libraries API and has a text field and submit button that evals the code and executes it immediately on the page.

Okay, it's nowhere near as immediate or as cool as Try Ruby, but.. I answered the question by writing a book, Beginning Ruby - http://www.amazon.com/Beginning-Ruby-Novice-Professional-Sec... (not an affiliate link). Ah well, I had to try!

I sense, though, your question is looking for something more immediate to get over the "why bother?" hump with people who claim to want to do something but if it requires more than an ounce of effort could give up easily. In which case.. I'd recommend Microsoft's Small Basic: http://msdn.microsoft.com/en-us/devlabs/cc950524.aspx

Get a linode slice and tell them to download putty. I made the switch to linux after a LONG time of just programming on windows (VBA activated excel sheets, more complicated than it sounds) and that is how I did it. I now program in Ubuntu, but when you are first starting out typing "ruby helloworld.rb" in putty is not too daunting.

http://utilitymill.com/utility/MetaUtility Just about the same thing for Python. It would probably be trivial to write another one like _why's with Rails, though