Wimodel is a project mainly written in Ruby, it's free.
Fun with performance Madeleine vs MySql - Ruby
A test of storage layer exchange in a project having 100M+ of data
Current storage: MySQL (around 200GB of innodb) Tested storage: Madeleine (Ruby Prevalence implementation)
Model taken from existing app
see INSTALL for detailsruby test_me.rbhosted on github