What is "xapian"

Xapian is an open source probabilistic information retrieval library, released under the GNU General Public License (GPL). It is a full text search engine library for programmers.

It is written in C++, with bindings to allow use from Perl, Python, PHP, Java, Tcl, C#, Ruby, and Lua. Xapian is highly portable and runs on Linux, OS X, FreeBSD, NetBSD, OpenBSD, Solaris, HP-UX, Tru64, IRIX, Windows, Hurd, and OS/2.

Xapian is designed to be a highly adaptable toolkit to allow developers to easily add advanced indexing and search facilities to their own applications.

A growing number of organisations and projects are known to be using Xapian including Debian, Gmane, Die Zeit, Delicious, MoinMoin, and One Laptop per Child.