Boot-to-Basic is a fond memory for many of us, but booting to Forth, or Scratch, or any other language, fits the same kind of idea: how nice it might be, to have a device which boots into a self-contained programming environment, preferably instantly, and preferably without distractions. And it turns out, there are quite a few possibilities.
The CG Maximite powers on to BASIC and has composite video or VGA out.
The fignition has a composite out and powers on to forth.
There are software solutions too - emulators or web apps - which would serve the purpose, if only a device could be set up to run them at boot:
A curated list of available fantasy consoles/computers.
Via these two discussions on HN: