Rake
RVM allows you to run rake tasks across multiple ruby versions, for example:
$ rvm all do rake spec
or:
$ rvm 1.8.6,1.9.1 do rake spec
JSON Summary
Add a --json flag prior to the word 'do' and a JSON summary will be printed out at the end of the run.
YAML Summary
Add a --yaml flag prior to the word 'do' and a YAML summary will be printed out at the end of the run.