One Roll Engine

One Roll Engine, abbreviated as ORE is a fairly generic roleplaying system that has been adapted for various settings and games, the most notable adaptation has been the Reign fantasy RPG, the latest is Better Angels. ORE games usually use only d10, although the mechanic could work for other dice so long as you're careful to use appropriate-sized pools.

How

ORE uses pools of identical dice combined from inborn abilities (stamina, charm) and learned skills (sorcery, diplomacy), much like the Storyteller or Shadowrun. I.E.: swinging a chainsword is Strength+Melee, you have STR-2 and Melee-3, so you would roll (2+3=)5 dice. Once the dice are rolled you do not look for how many dice show a number higher than "X', nor add their values together; instead, you look for groups of dice that show the same number. For example if you roll 7, 4, 9, 7, 4 and 4, you have three sets: a one 9 set, a double 7 and a set of three fours. You pick one of these sets as the result of your roll.

In this way just one roll conveys two pieces of information: the width of the roll (how many dice are there in the set) and the height (the value on the face of dice in the set) in the set. In combat this shows the strength and the location of the hit. When using a skill this information tells you the quality and the speed of your work. In opposed rolls, the defender can use sets to remove dice from the attacker's sets until either the defender or the attacker doesn't have any matching pairs left.

This core mechanic is then expanded with various special dice (different games treat these in different ways). These specials let you set them to a specific number before you roll, or change them after you roll and so on. An expert die or hard die is like a called shot: you turn it to a certain facing, and then roll the rest. A wiggle or master die is more like a supernatural ability where it's impossible to fail: you set it aside before rolling, and then turn it to any facing after you roll (which guarantees at least one pair, or improves a success you already rolled).

Dice pools are never allowed to exceed the highest number on the dice used, else the pool would automatically have at least one pair. When using Stat+Skill to determine dice pools, this means the most points you can assign to a stat or skill is half (round down) the highest number in the dice you're using (ie. with d10, your pool can never exceed 10 dice, so nobody can have a STR stat higher than 5, nor Brawling skill greater than 5. If you were using d6, the max pool size would be 6 dice with max for stats/skills at 3...).

The only exception to the maximum size of dice pools is when ORE is used for character generation in Reign -- there you want to have at least one pair, so you roll 11d10 and the sets and singles that result give your character abilities, skills, previous careers and some historical background.

Math

# of d10	Percentage chance of width						d20 equivalent
	-	2	3	4	5	6	success	superb	critical
2d	90.00%	10.00%	-	-	-	-	19	-	-
3d	72.00%	27.00%	1.00%	-	-	-	15	>20	-
4d	50.40%	45.90%	3.60%	0.10%	-	-	11	20	>>20
5d	30.24%	61.20%	8.10%	0.45%	0.01%	-	7	19	>>20
6d	15.12%	69.12%	14.49%	1.22%	0.05%	0.00%	4	17	>20
7d	6.05%	68.80%	22.43%	2.55%	0.17%	0.01%	2	15	20
8d	1.81%	61.92%	31.25%	4.59%	0.41%	0.02%	1	13	19
9d	0.36%	51.30%	40.03%	7.42%	0.83%	0.06%	<1	11	19
10d	0.04%	39.54%	47.72%	11.06%	1.49%	0.14%	<<1	8	18

• Lester Ward goes further than you ever will with the dice probability thing.

Where

It is used in at least the following games:

• Godlike
• Wild Talents
• NEMESIS
• Reign
• starORE
• A Dirty World
• Monsters and other Childish Things
• Better Angels

Most of these games are written by Greg Stolze.