Alpine Linux

Parrot Linux, is a full Debian-based operating system, that is geared towards security, privacy and development. It is fully-featured yet light-weight, very open. There are 3 editions: General Purpose, Security and Forensic. The Secure distribution includes its own sandbox system obtained with the combination of Firejail and AppArmor with custom security profiles. While the Forensics Edition is bundled with a comprehensive suite of security/ pen-testing tools, similar to Kali and Black Arch.

Open-source security-oriented operating system for single-user desktop computing. It uses virtualisation, to run each application in its own compartment to avoid data being leaked. It features Split GPG, U2F Proxy, and Whonix integration. Qubes makes is easy to create disposable VMs which are spawned quickly and destroyed when closed. Qubes is recommended by Edward Snowden.

Tails is a live operating system (so you boot into it from a USB, instead of installing). It preserves your privacy and anonymity through having no persistent memory/ leaving no trace on the computer. Tails has Tor built-in system-wide, and uses state-of-the-art cryptographic tools to encrypt your files, emails and instant messaging. Open source, and built on top of Debian. Tails is simple to stop, configure and use.

Whonix is an anonymous operating system, which can run in a VM, inside your current OS. It is the best way to use Tor, and provides very strong protection for your IP address. It comes bundled with other features too: Keystroke Anonymization, Time Attack Defences, Stream Isolation, Kernel Self Protection Settings and an Advanced Firewall. Open source, well audited, and with a strong community - Whonix is based on Debian, KickSecure and Tor.