Recoll is a personal full text search package. It is based on a very
strong backend (Xapian), for which it provides an easy to use and
feature-rich interface.

Features:
 * Free, GPL license.
 * Easy installation, few dependencies. No database daemon, web server,
   desktop environment or exotic language necessary.
 * Will run on most Unix-based systems
 * Qt 5 GUI, plus command line.
 * Searches most common document types, emails and their attachments.
   Transparently handles decompression (gzip, bzip2).
 * Powerful query facilities, with boolean searches, phrases, proximity,
   wildcards, filter on file types and directory tree.
 * Multi-language and multi-character set with Unicode based internals.
 * Extensive documentation, with a complete user manual and manual pages
   for each command.

WWW: https://www.lesbonscomptes.com/recoll/