Amium - A collaboration app that brings conversation to your files
Spark Mail - Spark helps you take your inbox under control. Instantly see what’s important and quickly clean up the rest. Spark for Teams allows you to create, discuss, and share email with your colleagues
Dropbox Paper Mobile - Organize your team’s knowledge in a single place
TL;DR Email - Send short emails & read emails as fast as you read Facebook
Silent Inbox for Gmail - Receive unimportant emails and newsletters on your schedule
mlist - Email newsletters, outside of the inbox