The 
Greenstone Digital Library Software (GSDL) allows you to easily full-text index collections of documents and make them available over the Web. The plugin architecture makes it easy to add support for new file formats. Plugins (written in Perl) exist for formats such as text, HTML, MBox/MailDir mail format, PDF, RTF, MicrosoftOffice (.doc, .xls, .ppt), bibtex(1), PostScript, MARC records, and more.
The software is developed by the New Zealand Digital Library research group in the ComputerScience department at the UniversityOfWaikato. GreenStone is covered by the GPL and runs on MicrosoftWindows (version 3.1 and up) as well as POSIX systems such as MacOSX, Linux, Solaris, etc.
The WlugWiki has a GreenStone backed fulltext search.
