I know a former coworker who is maintaining 3-4 different desktop accounting packages on independent VMs, each on a different application and windows versions b

I know a former coworker who is maintaining 3-4 different desktop accounting packages on independent VMs, each on a different application and windows versions because different clients are attached to their particular rev of the accounting software. He got to this point because he was sick of working out how to get multiple versions of the software to play nice with one another. On the one hand this locks in Windows pretty tightly - on the other, the OS in the VM is just acting as a fat compatibility layer waiting to be replaced. I think he's moving on to experimenting with Wine next (or maybe this is a use case for Docker). This isn't some a large enterprise company either, just a small accounting consultancy trying to maintain client compatibility.