Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
Geary - Geary is an email application built for GNOME 3.
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.