Needle is a dependency injection (also, inversion of control) container
for Ruby. Ultimately, it can reduce the amount of code that you have to
write, simplifying many common programming tasks for you. This has the
two-fold benefit of both decreasing application development time, and of
decreasing the effort needed to maintain your application.

Specifically, Needle can do:

 - Log Method Execution
 - Reference Another Service
 - Unit Testing
 - Lifestyle Management

WWW: http://needle.rubyforge.org/