Ackr is a very small subset of grep/ack/rak, for lazy developers. grep is a great tool, a very powerful tool, but often too powerful for simple needs. Ackr looks for a search string in all text files and in all subfolders from the working directory, is case insensitive, has no options, doesn't look into hidden folders/files, and displays the search term in a bold font.
Coco is a code coverage utility for Ruby. It can be used from RSpec or unit/test with a simple "require 'coco'". It works with standalone Ruby or with Rails. It displays the names of files that are uncovered on the console, builds a simple HTML report, and reports sources that have no tests. It is UTF-8 compliant, configurable via a simple YAML file, and has colorized console output.
RubyTree is a simple to use general purpose tree data structure implementation in Ruby. It provides easy access methods for navigating the hierarchy, as well as for accessing the nodes. It also provides ability to marshal the entire tree structure. The library provides a generic tree as well as a binary tree implementation. It is available as a RubyGem or standard Tar/ZIP packages.
AffirmIt! is a supportive testing framework for Ruby. It tolerates all code, whether it exhibits behavioral challenges or not. It never uses the words "test" or "failure", which would imply a value judgment, or "assertions," which would imply an absolute truth. Instead, it treads softly around code and espouses preferences.