xanalogTV and the like run CRT effects even under an Athlon 2000 back in the day.
WIthout something bound to GL => 3.3 you can run a terminal emulator anywhere, even under legacy systems with no OpenGL support at all.
On the emulator from Lars in the below comment, that's a good approach; but for the physical CRT effects, as I said, XanalogTV did a great job.
But kudos for allowing a GL-less option for legacy systems.