Airmail is a fast mail client for Mac and iPhone.

Claws Mail is a free and open-source, GTK+-based email and news client. It offers easy configuration and an abundance of features.

K-9 Mail is an open source email client with support for multiple accounts, search, IMAP push email, multi-folder sync, flagging, filing, signatures.

Mailbird is a desktop email client for Windows 7, 8 and 10.

Mailspring is a multi-platform email client.

Thunderbird is a open source mail client developed and maintained by Mozilla foundation.

Apple Mail is an email client included with the operating systems macOS, iOS and watchOS by Apple Inc.

eM Client is a Windows based e-mail client for sending and receiving e-mails, managing calendars, contacts, and tasks.

Microsoft Mail and Calendar apps help you stay up to date on your email, manage your schedule and stay in touch with people you care about the most.

MailMate is an IMAP email client for macOS featuring extensive keyboard control, Markdown integrated email composition, advanced search conditions.

Microsoft Outlook is a personal information manager from Microsoft.

OpenProject is a web-based project management system for location-independent team collaboration.