Befunge - Wikipedia

Befunge is a stack-based esoteric programming language which differs from conventional languages in that programs are arranged on a two-dimensional grid. 'Arrow' instructions direct the control flow to the left, right, up or down, and loops are constructed by sending the control flow in a circle. This technique is demonstrated in the random number generator program below:

 vv  <      <
     2
     ^  v<
  v1<?>3v4
     ^   ^
 >  >?>  ?>5^
     v   v
  v9<?>7v6
     v  v<
     8
  .  >  >   ^
 ^<

Instructions in Befunge:
`0-9`	Push this number on the stack
`+`	Addition: Pop a and b, then push a+b
`-`	Subtraction: Pop a and b, then push b-a
`*`	Multiplication: Pop a and b, then push a*b
`/`	Integer division: Pop a and b, then push b/a, rounded down. If b is zero, ask the user what result they want.
`%`	Modulo: Pop a and b, then push the remainder of the integer division of b/a. If b is zero, ask the user what result they want.
`!`	Logical NOT: Pop a value; if the value is zero, push 1, otherwise zero.
`	Greater than: Pop a and b, then push 1 if b>a, otherwise zero.
`>`	Move right
`<`	Move left
`^`	Move up
`v`	Move down
`?`	Move in a random direction
`_`	Pop a value; move right if value=0, left otherwise
`\|`	Pop a value; move down if value=0, up otherwise
`"`	Start string mode: push each character's ASCII value all the way up to the next `"`
`:`	Duplicate value on top of the stack
`\`	Swap two values on top of the stack
`$`	Pop value from the stack
`.`	Pop value and output as an integer
`,`	Pop value and output as ASCII character
`#`	Trampoline: Skip next cell
`g`	Pop y and x, then pushes ASCII value of the character at that position in the program
`p`	Pop y, x and v, then change the character at the position x/y in the program to the character with ASCII value v
`&`	Ask user for a number and push it
`~`	Ask user for a character and push ASCII value
`@`	End program

The language was originally created by Chris Pressey in 1993, as an attempt to devise a language as hard to compile as possible - note that the 'p' command allows for self-modifying code. Nevertheless, a number of compilers have subsequently been written. A number of extensions to the original 'Befunge-93' specification also exist, including Funge-98, which extends the concept to an arbitrary number of dimensions and can be multithreaded, with multiple instruction pointers operating simultaneously on the same space.