REXML is an XML 1.0 compliant, reasonably fast, non-validating XML parser. It has an API that is designed to be intuitive, straightforward. and terse. REXML includes a tree model parser, a SAX2 streaming parser, and a pull parser. It also includes a full XPath implementation. All of REXML's parsers pass 100% of the Oasis XML non-validating tests. As of Ruby 1.8.0, REXML is distributed with Ruby.
MetaRuby contains miscellaneous libraries (useful now) for a future Ruby-in-Ruby interpreter including Array/Hash/String as abstract ("Hollow") classes, an undo queue, a statistical time-profiler, an event loop, a modular marshaller ("ToSource"), a specification for a modular+reflexive+homoiconic remote call system ("LGRAM"), a declarative type system, a schema for expressing Ruby source code as proper (non-special) Ruby objects, etc.
GridFlow is a plugin for PureData, Ruby, and jMax. It provides the ability to process images and video as N-dimensional arrays ("Grids"). It consists of a framework for grid transmissions, elementary grid processing objects, picture-oriented processing objects, and input/output objects. It also allows one to write plugins for PureData and jMax using the Ruby language.
The PLEAC project aims to re-implement the solutions presented in the Perl Cookbook (by Tom Christiansen & Nathan Torkington, published by O'Reilly) in other programming languages. If successful, this project may become a primary resource for quick, handy, free solutions to most common programming problems using higher-level programming languages. It could also be useful for comparison on ease-of-use and power/efficiency of these languages.