<sigh> Not a single tool we use is open source. Mainly because with an open source application there's no one source for security to go to and ask for a letter certifying the safety of the software.
I'm not the original poster, but I find it slightly humorous at the incredulity of not running open source software anywhere. 15 years ago nobody would have batted an eyelid.
Back in the "dark days", I worked for a couple of Microsoft Certified Partners. One of the things they all had in common was a "no open source" policy. I wasn't even allowed to run emacs as my editor. GPL was explicitly "evil" and even more permissive licenses were "evil enough". Hell, I had to use Visual Source Safe for version control! I would have killed for RCS, let alone something like Subversion.
And, no, not a single Linux box, or even BSD system to be found. Every single server was running Windows. I remember noticing strange network traffic one time and, lacking the tools in Windows, booted up Knoppix and diagnosed the problem -- a former employee had set up a program on an idle machine to forward the source code for our software outside the company. I couldn't tell the network admins how I had found the problem because it was more than my job was worth to admit to having used GPL software on the premises.
Of course, I don't work for companies like that any more. In fact, I'm gratified to discover that they are so rare that nobody believes they could possibly exist. In my current job, apart from 3 SaaS products (Github, Trello and Slack), every single tool I use is open source. I sometimes have to pinch myself to make sure I'm not dreaming...
Nope, not that I'm aware of. Everything is Windows Server.
We had an application from one of our system vendors that incorporated FFmpeg for playing video streams within the app. We had to go and ask them to remove FFmpeg and replace it with some other video package that IT security approved of.
This is normal for my industry. It's kind of depressing. I hear about all these nice open source tools (pandas! numpy! for a couple of examples) and have to make do with closed source equivalents I like much less (MATLAB).