FnordMetric is a highly configurable (and pretty fast) realtime app/event tracking thing based on ruby eventmachine and redis. You define your own plotting and counting functions as ruby blocks! See it in action! (RailsCasts)
See master branch
gem install fnordmetric
or in your Gemfile:
gem 'fnordmetric', :git => 'git://github.com/umdstu/fnordmetric.git'
See master branch