Befunge

A 2d programming language named after a spelling of "before".

Instructions

Cmd	Description
+	Addition: Pop two values a and b, then push the result of a+b
-	Subtraction: Pop two values a and b, then push the result of b-a
*	Multiplication: Pop two values a and b, then push the result of a*b
/	Integer division: Pop two values a and b, then push the result of b/a, rounded down. According to the specifications, if a is zero, ask the user what result they want.
%	Modulo: Pop two values a and b, then push the remainder of the integer division of b/a.
!	Logical NOT: Pop a value. If the value is zero, push 1; otherwise, push zero.
`	Greater than: Pop two values a and b, then push 1 if b>a, otherwise zero.
>	PC direction right
<	PC direction left
^	PC direction up
v	PC direction down
?	Random PC direction
_	Horizontal IF: pop a value; set direction to right if value=0, set to left otherwise
|	Vertical IF: pop a value; set direction to down if value=0, set to up otherwise
"	Toggle stringmode (push each character's ASCII value all the way up to the next ")
:	Duplicate top stack value
\	Swap top stack values
$	Pop top of stack and discard
.	Pop top of stack and output as integer
,	Pop top of stack and output as ASCII character
#	Bridge: jump over next command in the current direction of the current PC
g	A "get" call (a way to retrieve data in storage). Pop two values y and x, then push the ASCII value of the character at that position in the program. If (x,y) is out of bounds, push 0
p	A "put" call (a way to store a value for later use). Pop three values y, x and v, then change the character at the position (x,y) in the program to the character with ASCII value v
&	Get integer from user and push it
~	Get character from user and push it
@	End program
0 – 9	Push corresponding number onto the stack

Examples

>              v
 v"Hello World!"<
 >:v
 ^,_@

~:1+!#@_,

&#::_.@#

I won't explain what those do :)