I've often wondered about taking this one step further: rather than using the terminal to render ersatz graphics, building a plain-text based, conversational operating system. Something like a generalization of ed[0], not just for editing but for doing every other task, but with a more verbose English syntax rather than line noise.

You could even do conversational tree editing, e.g.:

  Current node: function definition `fibonacci` with one parameter.

  >rt

  The return type is `int`.

  >body

  Current node: an `if` statement.

  >condition

  The condition is: n <= 2.

  >replace <= with <

  The condition is: n < 2. No type errors.

  >build and test

  Build complete. 100% tests pass.

Or something like an interactive fiction/text adventure[1] type thing, where you move through a virtual memory palace by typing e.g. "go east", "go up", and perform operations on data by using verbs like take, search, look up, etc.

[0]: https://en.wikipedia.org/wiki/Ed_(text_editor)

[1]: https://en.wikipedia.org/wiki/Interactive_fiction