mod_filter allows you to filter output from other modules inside of Apache. This allows you to implement filters (think Swedish Chef, jive, etc.). You can also use it to retailer output for your locale. This works with HTML documents, mod_perl, PHP, JServ, CGIs, and for that matter just about any sort of custom handler you might have.
NetCrawler is the frontend to a Web crawling system. This command line application will download all of the pages within a domain, and then parse and process all of the relative content (Images, Text, Audio, Video), saving this content within an XML document for later processing. It is definitely alpha quality, but has been used quite extensively.
Dynamator solves the server pages maintenance problem by completely separating HTML from server code for any technology. It merges pure, standard HTML with server code stored in separate XML files to produce standard server pages in technologies like JSP, XSL, PHP, and Java. Benefits include a more agile HTML UI, a streamlined internationalization and customization processes, easier reuse, and more efficient code.
Ganglia is a scalable distributed monitoring system for high-performance computing systems such as clusters and grids. It is based on a hierarchical design targeted at federations of clusters. Ganglia is currently in use on over 500 clusters around the world and has scaled to handle clusters with 2000 nodes.
Silva is a CMS for organizations that manage multiple or complex Web sites. Content is stored in clean XML, independent of layout and presentation. Features include versioning, a workflow system, an integral visual editor, content reuse, sophisticated access control, multi-site management, extensive import/export facilities, fine-grained templating, and hi-res image storage and manipulation. Silva is built on top of the Zope Web application platform.
xSiteable is a complete all-you-need package for creating sites that are fully relational, open source, fully templating-enabled, using only XML-based technologies to help you create complex sites on the fly. It packs such features as topic maps, notation for content, and the fast Sablotron xslt parser.
htmlArea is a free WYSIWYG editor replacement for common textarea fields in HTML forms. Users can change the font size/color, make it bold/italicized/underlined, add bullets and numbering, insert images and links, and more. It works with any server-side software that accepts forms, including PHP, ASP, Perl, etc., and enables users to format their content as easily as if they were using a word processor. No HTML knowledge is required. Once the form is submitted, the raw HTML is passed along through your CGI script for use in your program.