The Silver Searcher - A code searching tool similar to ack, with a focus on speed.
Mu4e - Starting with version 0.9.8, mu provides an emacs-based e-mail client which uses mu as its back-end: mu4e.
grep - grep is a command-line utility for searching plain-text data sets for lines matching a regular...
Mutt - Mutt is a small but very powerful text-based mail client for Unix operating systems.
dnGREP - dnGrep allows you to search across files with easy-to-read results.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.