KeePassXC - KeePass Cross-Platform Community Edition - A community maintained fork of the popular KeePassX...
VeraCrypt - VeraCrypt is a free open source disk encryption software for Windows, Mac OSX and Linux.
Kleopatra - Kleopatra is a certificate manager and GUI for GnuPG.
Windows BitLocker - This topic provides a high-level overview of BitLocker, including a list of system requirements, practical applications, and deprecated features.
Seahorse - Front end for GnuPG.
Knox - Knox offers easy disk image encryption and comes with a built-in backup service.