Is it possible to use a serial terminal (e.g. VT420) with a modern Mac?
I have not tried this, personally, but there are good instructions for doing so with a Tripp Lite (née Keyspan) USB-to-Serial adapter and an Apple IIc. Obviously, you can ignore the Apple II-specific parts of the instructions (the majority of the article) and focus on the adapter, the cable, and getting ttys to run getty.