RAML is a Ruby-syntax-based data language.

Ratch is a Ruby-based batch scripting language. It's a DSL over regular Ruby to make the life of the batch script writter easier.

R.C. is a multi-tenant runtime configuration system for Ruby projects. It can be used to configure almost any Ruby tool or library regardless of whether that tool or library has dedicated support for RC or not.

Real makes true reflection possible for Ruby objects. This can be important to metaprogrammers who need to ensure they have the true information.

RSpecial defines a set of RSpec-compatible matcher methods which are BRASS compliant by using Assay as a backend. This allows developers to switch to BRASS compliant test frameworks without having to change a slew of previously written RSpec-based specifications.

This tool allows you to easily deploy applications to servers. Though currently only Java WARs and Tomcat servers are supported ;-)

Rubytest is a universal test harness for Ruby. It can handle any compliant test framework, even running tests from multiple frameworks in a single pass.

Rulebow is an automated build tool with a set-logic based rule system. Rulebow is the perfect tool for performing continuous integration during development.

String::Mask provides a kind-of string algebra useful for manipulating strings in comparitive ways, eg. add, subtract, xor, etc.

Interactive runner for qed tests

TkXML translates XML markup into Ruby Tk interface code

A TracePoint is a Binding with the addition of event information. Among other things, it functions very well as the join-point for AOP. In practice it provides a better alternative to using set_trace_func.

The Versus gem provides a solid Version class along with supporting functionality, such as version constratints and version dependency resolution.

XOXO is a Ruby XOXO parser and generator. It provides a Ruby API similar to Marshal and YAML (though more specific) to load and dump XOXO[http://microformats.org/wiki/xoxo], a simple, open outline format written in standard XHTML and suitable for embedding in (X)HTML, Atom, RSS, and arbitrary XML.

YAML Easy Schemas it a straight-foward but powerful YPath-based schema format and validation program for YAML documents.