I love to use open source and free softwares. For email client, I use Mozilla Thunderbird and for instant messaging client, I use Pidgin.
Mozilla Thunderbird is a free, open source, cross-platform e-mail and news client developed by the Mozilla Foundation.
Pidgin (formerly named Gaim) is a multi-platform instant messaging client, based on a library named libpurple. Libpurple has support for many commonly used instant messaging protocols, allowing the user to log into various different services from one application.
Both of them are multi-platform / cross-platform softwares. So, they can be installed in Linux, Windows, and other OS.
I am not going to discuss about their installation. Instead, this article shows how to minimize them to tray after they have been installed and are in use.
Minimize Thunderbird to Tray
– Install MinimizeToTry Plus addon.
MinimizeToTray Plus is an extension that makes it possible to minimize Firefox, Thunderbird and other Mozilla based applications to the system tray.
Addon URL: https://addons.mozilla.org/en-US/thunderbird/addon/minimizetotray-plus/
Minimize Pidgin to Tray
– Open Pidgin.
– Go to Tools -> Preferences
– Set Show System Tray to always
Hope this helps. Thanks