AXPbox is a fork of the discontinued es40 emulator. It could theoretically used for running any operating system that runs on the OpenVMS or Tru64 PALcode (e.g. OpenVMS, Tru64 UNIX, Linux, NetBSD), however as of now only OpenVMS and some versions of NetBSD can be installed (for more details see Guest support).
The emulator supports SCSI, IDE, serial ports, Ethernet (using PCAP) and VGA graphics (using SDL).
OpenVMS 8.4 desktop in AXPbox. Here is a wiki page showing you how to get this CDE desktop running
Pre-built binaries for generic Linux amd64, Windows 10 amd64 and macOS amd64 are available for each release, and also as artifacts produced for each commit in CI. T2 SDE has an official package for AXPbox, and openSUSE's Emulators project has an AXPbox package, too. The former gets updated the same day when a release happens, while requests are submitted now the latter that undergo approval of Emulators maintainers.
You can also build from source using CMake; you need a C++ 11 compiler, optional dependencies are PCAP for networking and SDL or X11 for graphics support.
First invoke the interactive configuration file generator:
axpbox configure
This creates a file named es40.cfg, which you can now modify (the generator UI doesn't allow to set all options). After the configuration file and the required ROM image are ready, you can start the emulation:
axpbox run
Please read the Installation Guide for information to get OpenVMS installed in the emulator. A guide for NetBSD is also available on the Wiki