CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/85-based microcomputers by Gary Kildall of Digital Research, Inc. Initially confined to single-tasking on 8-bit processors and no more than 64 kilobytes of memory, later versions of CP/M added multi-user variations and were migrated to 16-bit processors.
Some very cutting edge software was on CP/M including Wordstar, dBaseII and Supercalc.
You can run your own version of CP/M using an affordable Raspberry Pi. There seems to be variants out there, but cpumem appears to be a great choice.
CPMemu is a CP/M 2.2 emulator running on the Raspberry Pi and on other Linux systems. On the Raspberry Pi CPMemu can be used as a bare metal solution based on the Circle environment.
Currently CPMemu does not implement a specific set of terminal control sequences. Instead it sends all characters unchanged to the console.
Once you have your operating system up and running, you can jump to The Unofficial CP/M Web site to get all kinds of software and documentation thanks to the work of Tim Olmstead. Some additional emulators are listed on the site.