qTox
qTox is a free and open source instant messaging client with support for text, voice, and video chats, using the encrypted Tox protocol
Gajim
Gajim is a free and open source, multi-platform, easy-to-use, and full-featured XMPP client
Mailspring
Mailspring – free and open source, multi-platform fast desktop mail client
KMail
KMail is a free and open source email component of Kontact, an integrated personal information manager from KDE
Sylpheed
Sylpheed is a free and open source, multi-platform, simple and lightweight email client
Evolution
Evolution is a free and open source application for managing personal information: mail, contacts, calendar, tasks, and notes
Claws Mail
Claws Mail is a free and open source, lightweight and easily customizable email client and news reader based on GTK+
VGrive
VGrive – free and open source Google Drive client with automatic synchronization for Linux
OnionShare
OnionShare is a free and open source, multi-platform program that allows you to securely and anonymously share files, host websites, and communicate with friends using the Tor network
MEGA
MEGA – free program for syncing and backing up data to cloud storage MEGA.nz