IBM made a wide variety of unusual terminals over the years, and one example is the IBM 3151 ASCII terminal, which was manufactured to be a cheaper terminal for use in a variety of situations and to allow users to connect to a range of IBM and other brands of mainframes, the 3151 terminal used a cartridge to emulate other terminals.
A YouTube video review of the terminal by Norbert Kehr, who goes into a lot of detail about how to connect the terminal to a mainframe, both real and virtual, and also provides a history lesson on the use of block mode and character mode on these older terminals.
Additionally, Kehr explains how to get a virtual mainframe to run the terminal, although it does require a long list of emulators and other virtual machines to get it to work.
For those who are really keen, there are ways to build your own mainframe, or you could try to get an old IBM 3745.
