free text indexing tools

Thanks to Ben Gross...

Managing Gigabytes (no longer maintained, GPL)
http://www.cs.mu.oz.au/mg/

mifluz (pretty generic, GPL)
http://www.gnu.org/software/mifluz/

mnoGoSearch (mostly for Web content, but could be adapted, GPL)
http://search.mnogo.ru/

Cheshire II project (data needs to be in SGML/XML format, license unknown,
but free)
Work is in progress to make a distributed version.
http://cheshire.lib.berkeley.edu/

Alkaline UNIX / NT Search Engine (only free for non-commercial use)
http://www.vestris.com/alkaline/

Lucene
http://lucene.sourceforge.net/