If you're checking out jEdit, don't miss it's Ruby Editor Plugin which
supports method completion for Ruby core types, has an integrated RDoc
viewer and an auto-indent and insert 'end' feature:
http://www.jedit.org/ruby/

> *  Cross platform.
Yes, jEdit runs on the JVM, hence works in GNU Linux, Mac OSX, Windoze

> *  Multiple Document Interface
Able to put in screen splits both horizontally and vertically, as many
times as needed.

> *  Debugging = not needed.  Just a good editor
No debugging in the plugin yet, but editing is good.

> *  snappy.
Performs well on recent cpu machines.

The plugin is actively developed and supported by yours truely; if you
have any feedback send me a mail.

cheers,
Rob