Give creating an esoteric language a go, they're even more fun to build and play around with. Though in my personal attempts the interpreters always wind up being a chaotic train wreck of code.

My latest toy language has been QuackQuack, a language consisting of ducks. There's a sandbox there to play around.

http://vild.org/labs/quackquack/

tl;dr It's a lisp with the operator outside the parentheses.