Back in ~2001, me and my colleague (both young, self-taught devs) were very annoyed that the whole company had setup shop on Microsoft. It was especially MS SQL that we had a hard time with. It was slow, expensive and lacked features.
So in our spare time, we created a version of the entire website running on a free, faster MySQL.
The IT manager hated it, and the owners blocked it. Looking back, we were surrounded by Microsoft "fanboys", so even "cheaper + faster" didn't reach through.