I discovered OpenVMS. This is the real thing (I used to have an account on a University VAX/VMS system in the early 1980s).
The system can be run in an emulator (FreeAXP, SimH, and PersonalAlpha are all free). To accomplish this, you have to install an emulator and get it running. Then you have to get installation media and a hobby license. The hobby license can be obtained by telnetting to eisner.decus.org and logging in as "registration", and then typing in your member number at OpenVMS Hobbyist. Getting the installation media is a little more difficult, as HP does not allow it to be downloaded.