Trillian is a proprietary multiprotocol instant messaging application.

Postbox is powerful, intuitive, ultra-customizable, speedy task manager.

The Bat! is an email program for Windows that protects the correspondence and empowers the users to handle large amounts of emails quickly and efficiently.

POP Peeper is an email notifier that runs in your Windows taskbar and alerts you when you have new email on any of your accounts.

MailStore lets you archive your private email from almost any email source and search through them extremely quickly.

Foxmail is a freeware e-mail client.

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

Mailpile is a webmail client with encryption and privacy features built-in. Mailpile is free and open-source software.

Mutt is a text-based email client for Unix-like systems.

Kopano is an open-source groupware application suite originally based on Zarafa.

hMailServer is a free open source email server for Microsoft Windows.