Hackable (Software) Things

I like hackable things. I'll keep that vague, because I am in a vague mood.
See if you can spot the common theme:

1. Emacs
2. TeX / LaTeX
3. Forth (interactive on an MCU)
4. Snabb Switch
5. Smalltalk  (Squeak)
6. Unix command line (awk, sed, kornshell, bourne shell, maybe bash, etc)

Okay... why?

They are worlds at my fingertips.

They don't use XML.

They are extensible.

I can make them do useful things.

With the exception of #3 (Forth), none really manipulate the "physical world".

Speaking of Forth... having shipped a few professional devices built with Forth, I still haven't found anything nearly as useful or fun for MCU work.

Something I would love to have for embedded MCU work:

A nice REPL / Editor environment (host side, please) for manipulating/deploying eLua on MCUs. 

eLua has poor interactivity support, but I wonder if remotely instrumenting it is a better approach... maybe via ZeroBrane or Emacs?