Writing Games with Emacs by Zachary Kanfer. (video)
From the description:
Games are a great way to get started writing programs in any language. In Emacs Lisp, they’re even better—you use the same exact techniques to extend Emacs, configuring it to do what you want. In this presentation, Zachary Kanfer livecodes tic-tac-toe. You’ll see how to create a basic major mode, make functions, store state, and set keybindings.
You can grab the source code at: zck.me.
Ready to build some muscle memory?