Pie

Pie is an 2-dimensional esoteric programming language created by User:InfiniteDonuts that is sort of a Befunge/PATH hybrid. Like Befunge, it has strings and uses a stack for memory operations, and both arrows (like Befunge) and mirrors (like PATH and SNUSP) can be used for program flow. It currently has no interpreter.

Instructions

Instruction	What it does
/ or \	Mirrors
< > ^ v	Go left, right, up, or down, respectively
!	Skip the next instruction
?	If the number on top of the stack is 0, skip the next instruction.
+	Pop two values, then push their sum onto the stack.
-	Pop two values, then push their difference onto the stack.
*	Pop two values, then push their product onto the stack.
/	Pop two values, then push their quotient onto the stack.
"	Toggle string mode.
#	Print the top item of the stack as a number and pop it.
&	Get input and push it onto the stack.
Any number	Push it onto the stack.

Computational class

As Pie can only access the top of the stack, it is a push-down automaton.