I'm writing this post with an interesting tool called Dasher. It lets me navigate through textual spaces with any pointer device like a mouse, joystick, or eye tracker. Also, it learns as I type with it, so it organizes the space in accordance to my writing style. It even has a special LaTeX mode! It guides you though the text space, scaling elements according to probability.
I've been trying various accessibility options for writing with one hand like T9, but most of them are proprietary.
Perhaps my next project should be to implement a Lisp mode for Dasher and integrate it with Emacs.