Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Glympse - Glympse is the easy way to safely share your location in realtime. No sign-up needed.
Geary - Geary is an email application built for GNOME 3.
Zenly - Zenly is a GPS tracker to locate your friends in realtime.
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.
OwnTracks - Cross-platform location sharing