Top 20 products relevant to Calendar and Enterprise Communication

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.

Open Source

Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!

Native email app for email productivity.

Mailbird is the best email client for Windows 7, 8 and 10.

Airmail is a lightweight and lightning fast mail client for Mac.

eM Client is a fully-featured email client for Windows and macOS with a clean and easy-to-use interface. eM Client also offers features for calendars, tasks, contacts, notes, and chat. .

freemium

Mailspring is a mail client for Mac, Windows and Linux.

Open Source

KerioConnect is a commercial mail and groupware server.

Apps/Evolution - GNOME Wiki!

The Power Email App for busy professionals, like you.

Privacy-aware email app for Mac & iOS.

Claws Mail is an email client (and news reader), based on GTK+, featuring Quick response.

K-9 is an opensource email client making it easy to chew through large volumes of email.

Geary is an email application built for GNOME 3.

nPOPuk is an ultra-small, but comprehensive, e-mail client that runs on a wide range of...

Secure Email Gateway.

Displays new emails and the sender's contact photo, get notifications or even listen, read or...

TypeApp - The best Android and iOS email app ever created for mobile devices. Fast, simple and easy, TypeApp is the best email app for Android and iOS.

POP Peeper is an email notifier that runs in your Windows task bar and alerts you when you have new...

is a highly customizable browser extension that notifies you about the incoming emails from all your Google-Mail accounts and labels. Gmail notifier is available for Firefox, Chrome, Opera and Safari.