I once created an emulator for HP Time-Shared BASIC (https://en.m.wikipedia.org/wiki/HP_Time-Shared_BASIC) so I could run the original code for the original text-adventure form of Oregon Trail. I already had much of the AST parsing infrastructure in place for a syntax highlighting text editor I had written. The text editor component got extended to be the terminal emulator. This was all in JavaScript, rendering with Canvas2D, so that the resultant image could be textured into a 3D model of a Commodore PET (the only "old" computer model I could find that didn't cost an arm and a leg to download) in WebGL, then displayed in a VR headset through WebVR.

I regret nothing.