mspire - 'Mass Spectrometry Proteomics in Ruby' is a collection of tools for working with MS proteomics data in ruby. It seeks to support and add functionality for open standards (mzData, mzXML, Peptide/Protein Prophet and the TPP) and other formats.
RMMSeg is an implementation of MMSeg algorithm in Ruby. MMSeg is a Chinese segmentation algorithm based on two variants of maximum matching. RMMSeg can be used as a stand alone program or as an Analyzer of Ferret.
AFTER is a configurable test engine written in Ruby. Libraries can be added to facilitate testing against any application type. It also allows for test scripts to be written in any format provided there is an associated script reader for that format.
KirbyBase is a small, plain-text, DBMS written in Ruby. It can be used either embedded or client/server. It aims to be as "Ruby-ish" as possible. For example, queries are specified using Ruby code blocks, rather than SQL strings.
Nilsimsa, a locality-sensitive hash, in Ruby. From http://ixazon.dynip.com/~cmeclax/nilsimsa.html : "A nilsimsa code is [..] like a hash, but unlike hashes, a small change in the message results in a small change in the nilsimsa code."
ruby2c is a subset of the metaruby project, which aims at rewriting ruby's internals in ruby. ruby2c is the translation module and can automatically translate a method into equivalent C code for a subset of ruby. Very BETA, but making rapid progress.