Catfish is a search GUI powered by locate and find behind the scenes, with autocompletion from Zeitgeist and locate. The advanced options allow filtering by date and file type. The interface is intentionally lightweight and simple, using only GTK+. (GPL)
Linux - FreeBSD
Recoll is a personal full text search tool for Unix/Linux. It is based on the very strong Xapian search engine library, for which it provides a powerful text extraction layer and a complete, yet easy to use, Qt graphical interface. (GPL)
Linux - FreeBSD
regain is a search engine similar to web search engines like Google, with the difference that you don't search the web, but your own files and documents. (LGPL)
Cross-platform
3 applications