DOSBox-X: Free, cross-platform and complete DOS, Windows 3.x and 9x emulation
I have a fun anecdote involving DOSBox.Back in 2012 I worked at a large manufacturing company. They had an old IBM PC running IBM DOS which controlled a vital system at the beginning of their production line. This machine had been chucking along since 1992 and now someone high up had been made aware that it could be a potential risk if this machine stopped working. It was therefore decided that this PC should be replaced/upgrade if possible.After investigating I learned it communicated with a PLC through the RS-232 interface and ran some special sauce software from a company that stopped existing in 1995. Previous upgrade attempts involved virtualization, but that did not work since the program ran too quickly on modern hardware.My solution was to copy everything from the old HDD to a new computer, install DOSBox and configure the serial port. The first few attempts caused some sirens and alarms to go off in the building, which was "exiting", but after fiddling with the emulation speed I managed to get it to work.To this day, unless something drastic has changed, a billion $ company is running DOSBox in production (and I literally mean production).Also, a side note. The old PC was still connected to a modem with a dedicated phone line. At some point it had been remotely operated through some kind of Norton remote control software. I made sure to turn off the modem and did not bring it over to the new DOSBox setup. Imagine if someone had war dialed into the machine... They could have caused a major disturbance and potentially started a fire.