To be fair, a list of things obscure in 2022 will naturally be weighted to dated software that became obscure with age. I'm surprised to see xterm on the list, but I guess most people are using more modern terminals, or urxvt if they prefer it retro.
The obscure part of xterm for me was the built in tektronix (vector) terminal emulation. I remember digging up a .dvi viewer that could display on tektronix by drawing a _lot_ of horizontal lines.
