The original Celeste was written for the PICO8. This PICO8 emulator was then ported to run on the Ti-84CE. Then this Ti-84CE port of Celeste ("CEleste") was ported to Windows/Linux through a tool called PortCE. Then PortCE was ported to emscripten which is what you see below in this image
PICO8 --> Ti84CE --> Windows/Linux --> emscripten