Quanta + is an excellent Web development environment for Linux
It can also be installed on OS X through Fink
Quanta already has Ruby syntax support, it now also comes with Rails syntax support. For older version of Quanta rails syntax can be added to Quanta + (or any other linux app that makes use of the katepart syntax files) by saving, and copying this syntax file to
[kde prefix]/share/apps/katepart/syntax/rhtml.xml
Your kde prefix is usually /usr or /opt/kde3, it can easily be found with:
locate katepart
You can also put it in ~/.kde/share/apps/katepart/syntax/rhtml.xml
(especially if you you’re not root)