Open-ended D6 rolls implemented in various programming languages.
It works like this: You roll a six-sided dice. If you roll a 6, roll the dice again. If 4–6 is rolled, add 1 to the original roll (making it a 7) and roll the dice again, adding 1 to the original roll until you roll a 1, 2 or 3. If the original roll is a 1, roll the dice again, subtracting 1 from the original 1 if you roll 1–3. Keep rolling and subtracting until you end up rolling a 4, 5 or 6.Any two consequtive 1s indicates a "fumble" while two consequtive 6s indicates a "critical" roll.
There is no limit to the result you can get with an open ended dice roll, including negative results such as –5.
See the Amar RPG wbsite for more.
Original not for my own code: So far it seems to me that Forth is the most compact code, while Vimscript and Fortran are the most verbose, with Julia and Nim perhaps being the most humanly readable - although I prefer to program in Ruby and FOCAL.
And then a Julia thread popped up with lots of attack angles and really clever Julia code. I took one and included it here as O6-julia2.jl. This is so far the coolest I've seen as an O6 implementation.