QNX has been employed now on Blackberry 10 devices which I guess is also derived for Linux. It's not open source either, in fact, very much not so. People are going wild on Blackberries decision to EOL the Playbook tablet. People want to be able to install their own OS on to the tablet if they no longer will support it but Blackberry refuse for obvious reasons. The Playbook is still in use with the Canadian military and many government organisations. Can't see how wiping it and installing your own OS would affect them but there ya go.
Many hackers have tried to root the Playbook but as of yet I haven't heard of anyone who has. Blackberry built the security into the hardware so you could never get passed the bootup to be able to do anything. They're also incorporating QNX in cars that will communicate with your blackberry devices. Apparently QNX is used in nuclear power stations etc because it is very secure and stable, but again, it's still a type of linux.
