Flex is a tool for generating scanners: programs which recognized lexical patterns in text. It reads the given input files for a description of a scanner to generate. The description is in the form of pairs of regular expressions and C code, called rules. Flex generates as output a C source file, lex.yy.c, which defines a routine yylex(). This file is compiled and linked with the -lfl library to produce an executable. When the executable is run, it analyzes its input for occurrences of the regular expressions. Whenever it finds one, it executes the corresponding C code.

lighttpd is a small webserver and fast webserver developed with security in mind and a lot of features. It has support for * CGI, FastCGI and SSI * virtual hosts * URL rewriting * authentication (plain files, htpasswd, LDAP) * transparent content compression * conditional configuration * HTTP proxying and configuration is straight-forward and easy.

FlightGear Launch Control (FGRun) is a graphical frontend for running the FlightGear Flight Simulator (fgfs).

Pandoc is a Haskell library for converting from one markup format to another, and a command-line tool that uses this library. The formats it can handle include * light markup formats (many variants of Markdown, reStructuredText, AsciiDoc, Org-mode, Muse, Textile, txt2tags) * HTML formats (HTML 4 and 5) * Ebook formats (EPUB v2 and v3, FB2) * Documentation formats (GNU TexInfo, Haddock) * Roff formats (man, ms) * TeX formats (LaTeX, ConTeXt) * Typst * XML formats (DocBook 4 and 5, JATS, TEI Simple, OpenDocument) * Outline formats (OPML) * Bibliography formats (BibTeX, BibLaTeX, CSL JSON, CSL YAML, RIS) * Word processor formats (Docx, RTF, ODT) * Interactive notebook formats (Jupyter notebook ipynb) * Page layout formats (InDesign ICML) * Wiki markup formats (MediaWiki, DokuWiki, TikiWiki, TWiki, Vimwiki, XWiki, ZimWiki, Jira wiki, Creole) * Slide show formats (LaTeX Beamer, PowerPoint, Slidy, reveal.js, Slideous, S5, DZSlides) * Data formats (CSV and TSV tables) * PDF (via external programs such as pdflatex or wkhtmltopdf)

Relational is primarily a tool to provide a workspace for experimenting with relational algebra, an offshoot of first-order logic.

WordNet(C) is an on-line lexical reference system whose design is inspired by current psycholinguistic theories of human lexical memory. English nouns, verbs, adjectives and adverbs are organized into synonym sets, each representing one underlying lexical concept. Different relations link the synonym sets.