tbibtools provide a simple regexp-based BibTeX parser that can be used to sort bib files, reformat bib files, list keys in a bib file, and show bib entries matching a regular expression. It is available as both a script and a VIM plugin. It makes a few assumptions about how a bib file should look like.
Rextile allows you to build XHTML documents and entire Web sites with ease. You write text using Textile (a format much more concise than XHTML), automate document parts with Ruby scripting, and generate the site offline (the server gets static XHTML). Rextile was inspired by Xilize. It uses RedCloth to convert Textile to XHTML, erb to run script blocks, and Hpricot for DOM manipulation.
Tartan is a text parsing engine targeted at wiki text. The syntax specification is defined in YAML in the form of regex-based rules. It supports layering and multiple output types. Rules for Markdown to HTML are included, with optional layered extensions for tables. It is implemented in Ruby, but looking to have implementations in other languages.
index.rb is a general indexing framework for Ruby. With it, you can create collections of documents, then index and search them. The traditional inverted index is supported, as is Latent Semantic Indexing (LSI). Input documents may be stemmed, to make user queries more general. It also provides TextTiling to break input documents covering multiple topics into topic-specific sub-documents.
Rcss implements CSS-SSC (CSS Server-Side Constants) in Ruby. Its features include the processing of rich CSS files using ERB templates, server-side constants, and server-side classes (preliminary). It plugs-in seamlessly to any Rails application but also allows the processing of Rcss files off-line using a command line executable.
rwdgutenberg is a book reading tool. It can find text files, build lists of text files, auto read texts, has context sensitive help, and can submit bug reports with one click. Additional applets can be downloaded. It includes the rwdtinker framework, and should not require any other downloads. It only requires that Ruby be installed, and should work on all platforms.