Recoll

is a personal full text search tool for Unix / Linux. ​http://www.lesbonscomptes.com/recoll/

• based on the very strong Xapian search engine library
• powerful text extraction layer
• complete, yet easy to use
• Qt graphical interface.
• Recoll is free, open source, and licensed under the GPL.
• last update 2011-11-26 (now 2011/12/06)

Xapian

is an Open Source Search Engine Library ​http://xapian.org/

• released under the GPL
• writing in C++
• with bindings to allow use from Perl, Python, PHP, Java, Tcl, C#, Ruby and Lua (so far!)

• latest stable version is 1.2.7, released on 2011-08-10.