LibreOffice - Free office suite, open source, and compatible with .doc, .docx, .xls, .xlsx, .ppt, .pptx files. Updated regularly – download for free. Originally based on OpenOffice.org.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
ONLYOFFICE - ONLYOFFICE is a complete office and productivity suite.
Geary - Geary is an email application built for GNOME 3.
Apache OpenOffice - Apache OpenOffice is an open source, office document productivity suite.
The Bat - The Bat! is a secure desktop email client for Windows, designed to protect your correspondence against third-parties and to save your time.