This is a trimmed-down, subminiature version of the Primary Fantasy SRD rules (see license for more info) that has been designed to be quick and easy to play. The goal was to create a simpler game, but one where all of the resources of Primary Fantasy SRD (monsters, spells, adventures and equipment) could be used without conversion.
Stats
There are 3 stats : Strength (STR), Dexterity (DEX) and Mind (MIND).

Roll 4d6, drop lowest dice. Total remaining 3 dice and allocate to one of the stats. Repeat for remaining stats.

Stat bonus = (STAT-10)/2, round down.
Races
Humans get +1 to all skill rolls
Elves get +2 MIND
Dwarves get +2 STR
Halflings get +2 DEX
Classes
The classes are Fighter, Rogue, Mage, Cleric. Characters begin at Level 1.

Fighters wear any kind of armour and use shields. They have a +3 bonus to Physical and add +1 to all attack and damage rolls. This increases by +1 at 5th level and every five levels on
Rogues can use light armour. They have a +3 bonus to Subterfuge. If they successfully Sneak (usually sub+DEX, but depends on situation) up on a foe they can add their Subterfuge skill rank to the damage of their first attack
Magi wear no armour. They can cast arcane spells, and gain a +3 bonus to Knowledge
Clerics can wear light or medium armour. They cast divine spells and gain +3 bonus to Communication. A Cleric can Turn Undead with a successful Magic Attack. DC is the current Hit Points of the Undead. If the DC is exceeded by 10 it is destroyed. This can be used (2 + Level + MIND Bonus) times per day.
Skills
There are just 4 skills : Physical, Subterfuge, Knowledge and Communication. Roll higher than the given Difficulty Class to succeed.

Skill rank = your level + any bonus due to your class or race.
Skill roll = d20 + skill rank + whatever stat bonus is most applicable to the use + situation modifiers

For example, Climbing would use Physical + STR bonus. Dodging a falling rock is Physical + DEX bonus. Finding a trap is Subterfuge + MIND bonus. Disabling a trap is Subterfuge + DEX bonus.

Note that there are no “saving throws” in this game; use Physical + STR or DEX bonus for Fortitude and Reflex saves. Saving against magic (Will save) is usually MIND bonus + your level.
Magic
Magi can cast any arcane spell, and Clerics any divine spell, with a spell level equal or below 1/2 their class level, rounded up. They have access to all arcane spells in the SRD spell list.

Casting a spell of any kind costs Hit Points. The cost is 1 + double the level of the spell being cast:

Spell Level	0	1	2	3	4	5	6	7	8	9	
HP Cost	1	3	5	7	9	11	13	15	17	19	

This loss cannot be healed normally but is recovered after 8 hours rest. There is no need to memorize spells in advance.

Just because a character can cast any spell, doesn’t mean that they should. Choose spells that suit the character. Select one ‘signature’ spell per spell level from 1st upward that they prefer to use over any other. These spells are easier to cast due to familiarity, costing 1 less HP to use.

The Difficulty Class (DC) for all spells is 
10 + Caster Level + Caster's MIND bonus

Combat
Hit Points = STR Stat + 1d6/Level. If HP reach 0, unconscious and near death. Further damage directly reduces STR. If that reaches 0, death.

Roll d20 + DEX bonus for initiative order. Everyone can do one thing each turn; move, attack, cast a spell, etc.

Melee attack bonus = STR bonus + Level
Missile attack bonus = DEX bonus + Level
Magic attack bonus = MIND bonus + Level

Add attack bonus to d20 roll. If higher than your opponent's Armour Class (AC), it’s a hit. Natural 20 is automatically a critical doing maximum damage.

Fighters and Rogues can use DEX bonus + Level as Melee attack bonus instead if wielding a light weapon. Fighters and Rogues can wield 2 light weapons and attack with both in a round if they take a -2 penalty on all attack rolls that round. Rapiers count as light weapons, but you cannot wield two rapiers at the same time.

If the total bonus is +6 or more a second attack can be made with a -5 penalty. If the total bonus is +11 or more a third attack can be made at -10. For example, if the total bonus is +12, three attacks can be made at +12/+7/+2.

Add STR bonus to Melee damage, x2 for 2-handed weapons. 
Armour Class (AC) = 10 + DEX bonus + Armour bonus.
Other Hazards
Falling : 1d6 damage per 10', half damage on Phys+DEX save. DC=depth fallen in feet
Spikes : add +1 point to falling damage per 10' fallen, max +10
Poison : Phys+STR save to avoid or for half, depending on poison.    Effect varies with poison type.
Extreme Heat & Cold : If not wearing suitable protection, Phys+STR save once every 10 minutes (DC 15, +1 per previous check), taking 1d6 damage on each failed save.
Level Advancement
Encounter Level = Hit Dice of defeated monsters, or the given EL for the trap, situation, etc. Add +1 for each doubling of the number of foes. eg: 1 kobold = EL1. 2 kobolds = EL2. 4 kobolds = EL3, etc.

Add up the Encounter Levels (ELs) of every encounter you take part in. When the total = 10 x your current level, you’ve advanced to the next level. Reset the total to 0 after advancing.

Each level adds:
+1d6 to Hit Points
+1 to all attack rolls
+1 to all skills

If the level divides by three (i.e. level 3,6,9,etc.) add 1 point to STR, DEX or MIND.

Fighters gain +1 to their attack and damage rolls at levels 5,10,15,etc.

Clerics and Magi gain access to new spell levels at levels 3,5,7,9,etc.

Example
The 1st level adventurers have just completed a dungeon adventure, and defeated 5 EL1 encounters, an EL2 trap and the EL3 leader. That’s a total of EL10, so they all advance to level 2. They need to defeat another 20 Encounter Levels to reach Level 3.

Monsters
Name	Hit Dice	Armour Class	Attack	
Animal (small) eg Badger	HD 1d8+2 (6 hp)	AC 15	Claw +4 (1d2-1)	
Ankheg	HD 3d10+12 (28 hp)	AC 18	Bite +7 (2d6+7 plus 1d4 acid)	
Bugbear	HD 3d8+3 (16 hp)	AC 17	Morningstar +5 (1d8+2) or javelin +3 (1d6+2)	
Choker	HD 3d8+3 (16 hp)	AC 17	Tentacle +6 (1d3+3)	
Deinonychous (Raptor)	HD 4d8+16 (34 hp)	AC 16	Talons +6 (2d6+4)	
Dire Rat	HD 1d8+1 (5 hp)	AC 15	Bite +4 (1d4 plus disease)	
Dragon (young Red)	HD 13d12+39 (123 hp)	AC 21	Bite +20 (2d6+7) or breath 10d10 DC24 phys+DEX to dodge for half	
Dwarf	HD 1d8+2 (6 hp)	AC 16	Waraxe +3 (1d10+1) or shortbow +1 (1d6)	
Earth Elemental (large)	HD 8d8+32 (68 hp)	AC 18	Slam +12 (2d8+7)	
Elf	HD 1d8 (4 hp)	AC 15	Longsword +2 (1d8+1) or longbow +3 (1d8)	
Gargoyle	HD 4d8+19 (37 hp)	AC 16	Claw +6 (1d4+2)	
Goblin	HD 1d8+1 (5 hp)	AC 15	Morningstar +2 (1d6) or javelin +3 (1d4)	
Griffon	HD 7d10+21 (59 hp)	AC 17	Bite +11 (2d6+4)	
Halfling	HD 1d8+1 (5 hp)	AC 16	Shortsword +3 (1d6) or light crossbow +3 (1d6)	
Hellhound	HD 4d8+4 (22 hp)	AC 16	Bite +5 (1d8+1 plus 1d6 fire)	
Hill Giant	HD 12d8+48 (102 hp)	AC 20	Greatclub +16 (2d8+10) or rock +8 (2d6+7)	
Hobgoblin	HD 1d8+2 (6 hp)	AC 15	Longsword +2 (1d8+1) or javelin +2 (1d6+1)	
Human Commoner	HD 1d8+1 (5 hp)	AC 12	Dagger +1 (1d6+1) or sling +1 (1d4)	
Insect (small) eg Spider	HD 1d8 (4 hp)	AC 14	Bite +4 (1d4-2 plus poison)	
Kobold	HD 1d8 (4 hp)	AC 15	Spear +1 (1d6-1) or sling +3 (1d3)	
Ogre	HD 4d8+11 (29 hp)	AC 16	Greatclub +8 (2d8+7) or javelin +1 (1d8+5)	
Orc	HD 1d8+1 (5 hp)	AC 13	Falchion +4 (2d4+4) or javelin +1 (1d6+3)	
Owlbear	HD 5d10+25 (52 hp)	AC 15	Claw +9 (1d6+5)	
Rust Monster	HD 5d8+5 (27 hp)	AC 18	Antennae touch +3 (rust)	
Shadow	HD 3d12 (19 hp)	AC 13	Incorporeal touch +3 (1d6 Str)	
Skeleton Warrior	HD 1d12 (6 hp)	AC 15	Scimitar +1 (1d6+1) or claw +1 melee (1d4+1)	
Stirge	HD 1d10 (5 hp)	AC 16	Touch +7 (attach)	
Stone Golem	HD 14d10+30 (107 hp)	AC 26	Slam +18 (2d10+9)	
Troll	HD 6d8+36 (63 hp)	AC 16	Claw +9 (1d6+6)	
Werewolf (hybrid form)	HD 3d8+7 (20 hp)	AC 16	Claw +4 (1d4+2)	
Wight	HD 4d12 (26 hp)	AC 15	Slam +3 (1d4+1 plus energy drain)	
Wolf	HD 2d8+4 (13 hp)	AC 14	Bite +3 (1d6+1)	
Wyvern	HD 7d12+14 (59 hp)	AC 18	Sting +10 (1d6+4 plus poison) or Talon +10 (2d6+4) or Bite +10 (2d8+4)	
Zombie	HD 2d12+3 (16 hp)	AC 11	Slam +2 (1d6+1) or club +2 (1d6+1)	

Skills: All creatures have a bonus to all skills equal to their number of Hit Dice. If the creature is intelligent, add +3 to one skill. Add stat bonuses to suit and as logic dictates. This is intentionally kept open – if you need a sneaky bugbear, assign the +3 bonus to Subterfuge; if a warrior, give +3 to Physical; for a spell-caster assign the +3 to Knowledge or Communication and give levels of Mage or Cleric (see below).
Monster Advancement: To make a tougher monster, add more Hit Dice; each additional HD adds one to their skill and combat bonuses.  For each doubling of the Hit Dice, increase the dice size for attacks (ie, d4->d6, d6->d8, etc).
Alternatively, add class levels to intelligent monsters. Start with the base Hit Dice and add levels of Fighter, Rogue, Mage or Cleric as required.
Create your own: Assign Hit Dice (d8 for most things, d12 for Dragons and Undead).  Attack bonus and skill level = number of Hit Dice. If it's an intelligent critter, +3 bonus to one skill. Add stat bonuses to suit. 

Sample Characters
Morris, Human Rogue-1
STR 12 (+1), DEX 15 (+2), MIND 12 (+1)
hp 13, AC 15 (Studded Leather), Paired Shortswords, +0/+0, d6+1
Subterfuge +5, all others @ +2

Kendrick, Dwarf Fighter-1
STR 16 (+3), DEX 13 (+1), MIND 11 (+0)
hp 17, AC 17 (Chainmail + shield), Longsword +5, d8+4
Physical +4, all others @ +1

Cholmer, Elven Mage-1
STR 12 (+1), DEX 13 (+1), MIND 16 (+3)
hp 13, AC 11 (Robes), Quarterstaff +2, d6+1
Knowledge +4, all others @ +1
Spells: All 0 and 1st level arcane spells.

Barnabas, Halfling Cleric-1
STR 10 (+0), DEX 16 (+3), MIND 13 (+1)
hp 11, AC 18 (Chainmail), Morningstar +1, d8
Communication +4, all others @ +1
Spells: All 0 and 1st level divine spells.

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System Reference Document Copyright 2000-2003, Wizards of the Coast, Inc.; Authors Jonathan Tweet, Monte Cook, Skip Williams, Rich Baker, Andy Collins, David Noonan, Rich Redman, Bruce R. Cordell, John D. Rateliff, Thomas Reid, James Wyatt, based on original material by E. Gary Gygax and Dave Arneson.
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