CloudMagic for Mac VS Task Coach

Nylas Mail - The Nylas Cloud API powers your application with email, calendar & contacts features. Built-in features for better email, calendar, and contact management.

Todoist - Todoist is a to-do list that helps you get organized, at work and in life.

Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

MailClark - The Slack bot for external communications

EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.