Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
Polymail - Native email app for email productivity.
Standard Notes - A safe place for your notes, thoughts, and life's work
Airmail for iOS - One of the best Mac email clients, now on iPhone
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.