Turing Machines and Lambda Calculus are equivalent in power, but opposite in style, ways of formally describing computing. Imperative programming came from one and functional programming from the other. One of simplest... conceptually and in implementation... versions of Lambda Calculus is LISP. I'm guessing you already know what it can do. In Turing/Imperative Land, I suggested Forth comes closest to being simplest of very powerful languages.
There's probably implementations of all of these in all the others out there. I'm just saying Forth is a Turing-style language with LISP-like simplicity and benefits.
Yosefk's write-up is the definitive one for me, though, showing an intro, some amazing stuff about it, weird stuff, and reasons for ultimately not going with it. Link:
There's probably implementations of all of these in all the others out there. I'm just saying Forth is a Turing-style language with LISP-like simplicity and benefits.