I am familiar with Ruby on Rails. I think that is the best Framework for Web Development. Yesterday I installed JRuby. That is the Ruby language implemented in Java. It is pretty good. Here is the Homepage:
On the Download Page there is a bundle for Mac OS X, too.
The installation worked pretty smooth. After the installation you can use in the command line like that:
jruby -S --version
You can install the rails framework like that.
jruby -S gem install rails
and create a new project like that
jruby -S rails new blog
It works pretty good. And with JRuby you can directly access Java classes. You can import JAR files and take advantage of the whole Java world.