Comment by JoachimSchipper

You may be inspired by "Fork yeah" - https://news.ycombinator.com/item?id=16839529 - bcantrill on Solaris.

But that was a situation in which an earlier version was already open-sourced. You could consider reimplementing the system as open source, if IP rights and non-competes don't prevent it.

But accepting that the owners killed the system is likely to make you happier.