Cryptomator - Free client-side AES encryption for your cloud files. Open source software: No backdoors, no registration.
DiskCryptor - A full disk and partition encryption system for Windows including the ability to encrypt the partition and disk on which the OS is installed.
Linux Unified Key Setup (LUKS) - A full disk encryption system for Linux using dm-crypt as the disk encryption backend. Included by default in Ubuntu. Available for Windows and Linux.
Hat.sh - A cross-platform, serverless JavaScript web application that provides secure file encryption using the AES-256-GCM algorithm in your browser. It can also be downloaded and run offline.