It's an IBM RS/6000 desktop workstation, with a P/390 card set (2 cards that add a mainframe CPU and 128 MiB of RAM). The R/390 mention is referring to IBM's name for an RS/6000 with a P/390 installed.
Running VM/ESA (one of the IBM mainframe OSes, dates back to the 1960s, and yes, VM means virtual machine, and yes, it means the same thing as it does in PC-land - VM basically gives every user a VM of their own, running a special-purpose stripped down OS called CMS, and all services get VMs of their own, and any other IBM mainframe OS can run within a VM as well), which is the OS that this card set was primarily designed for (but not IBM's flagship mainframe OS - that is the MVS (means Multiple Virtual Storage, but it's so obtuse that many call it Man Vs. System), OS/390, z/OS lineage).
No, there is no reason to run this hardware - emulation is easier to set up, and is far faster. And, no reason to play with mainframe hardware, either, but hey.