https://wiki.itcollege.ee/index.php/Operating_systems

https://i-tee.itcollege.ee/

https://wiki.ubuntu.com/LTS

https://www.qubes-os.org/

https://www.securemessagingapps.com/

https://www.virtualbox.org/

https://en.wikipedia.org/wiki/Symbian

https://en.wikipedia.org/wiki/CyanogenMod

https://en.wikipedia.org/wiki/LineageOS

http://distrowatch.com/