I've seen "RJS" and "RJS templates" mentioned in passing in blog posts and tutorials. I did a search, but I'm still unsure about it. Is it a technology specific to Rails, rather than a standard like JSON or YAML?
I understand it's used for "generating JavaScript." Does it generate generic JS or Rails-specific JS requiring the Prototype and Scriptaculous libraries?
This Railscast gives a nice example of using RJS to add and remove form fields dynamically without hitting the server with an ajax call.
These RJS tips may also be helpful.