txt2html is a Perl program that uses the HTML::TextToHTML perl module to convert plain text to HTML. It supports headings, lists, tables, simple character markup, hyperlinking and is highly customizable. It recognizes some of the apparent structure of the source document (mostly whitespace and typographic layout) and attempts to mark that structure explicitly using HTML.
Ilib is an image manipulation library for developers. It's capable of reading and writing images (PPM/PGM, PNG, JPEG, GIF, XPM, BMP) and many drawing functions including drawing lines and text using any BDF (X11) font. It's great for generating GIFs/PNGs from a CGI or generating graphs. Ilib includes sample applications for generating graphs for HTTP access.log files and QuakeWorld server frag log files and a tool for creating image indices from a group of images.
WPP is a small perl5 script that allows preprocessing of HTML files. It allows you to define "variables", which are brief abbreviations for longer constructs, and include common HTML fragments. It's useful for giving a uniform layout to different HTML pages. It can be used in cgi-bin programs for automatic generation of pages. With less HTML code inside you can make more flexible cgi-scripts.
Data::Locations is a virtual file manager which allows you to write and read data (text and binary) to and from virtual files (think of bubbles). Moreover, this manager allows you to (recursively) define "magic" insertion points in these virtual files (bubbles inside other bubbles) which can be filled in (inflated) later (through a "straw", i.e., the object's reference), at any convenient time and in any order you like. Since this software acts purely in memory, there is no slowing down through costly file input/output (i.e., no temporary files).
The Date::Calc package consists of a (pure-Perl) wrapper which either loads Date::Calc::XS (a separate implementation in C and XS) or Date::Calc::PP (a pure-Perl implementation which is part of the Date::Calc package). The Date::Calc::XS and Date::Calc::PP modules perform all kinds of date calculations based on the Gregorian calendar (the one used in all Western countries today), according to relevant norms and standards: ISO/R 2015-1971, DIN 1355 and, to some extent, ISO 8601 (where applicable). The package is designed as an efficient toolbox, not a bulky ready-made application. It provides extensive documentation and examples of use, multi-language support, and special functions for business needs.
SoX is the Swiss Army knife of sound processing tools: it can convert sound files between many different file formats and audio devices, and can apply many sound effects and transformations, as well as doing basic analysis and providing input to more capable analysis and plotting tools.