World of Darkness
Statistics
Attributes and abilities work as they would normally, except that the anti-magic attribute is not used in this world, nor are the magical disciplines. Faith and willpower play a special role and are used, but not as attributes.
Note that this means some changes from the WoD perspective. Most notably, the charisma and appearance scores are combined into charisma, and dexterity is split in the triad agility, dexterity and reflex. To me this seems justified as most people define charisma as either manipulation or appearance, without any clear distinctions, and because dexterity is the most powerful physical attribute in the game. Limits on primary or secondary groups are waived.
Backgrounds are available as per the regular game, and cost two experience point per rank ('dot'). These can only be bought when you first create your character, at least usually.

Combat
This is resolved using the normal Simplex rules. Yes, that means there are no such things as soak rolls, but then I've never understood that concept anyway.

Special statistics
These include humanity, virtue, rage, gnosis, arete and of course willpower. Occasionally a test is required on these scores. Firstly, if the number of successes required exceeds the character's score, the roll may not be attempted. Obviously this applies if the score happens to be zero. The difficulty for these rolls is three more than the Storyteller difficulty; add two for each additional success required. Note that a natural roll of two indicates a botch (fumble), and a three indicates a failure. Twelve is an automatic success, as per Simplex rules.
For instance, a standard virtue test (three dice, difficulty six, one success required) means the test becomes rank three, difficulty eight; a roll of five or higher is required to succeed. If three successes were needed, the difficulty would have been twelve, so a roll of nine is needed.

Vampire: the Masquerade
Kindred start the game with 200 experience points. Disciplines cost ten points per rank if clan-related, fourteen if not, and twelve for Caitiff. Otherwise disciplines are handled normally with exceptions for potence and fortitude - each two points of potence add three points to the character's strength, and each point of fortitude adds one to the character's damage absorption rating.
Nosferatu will notice there's no appearance score. That's okay, just roleplay it out - kine will run from your hideousness just the same.
Many disciplines require that you roll a certain combination of attribute and ability for them to work. Try the same here, using a standard difficulty of fifteen, plus two per extra success needed, plus two per point storyteller difficulty is above six. Just because a Simplex ability is normally based on a certain attribute doesn't mean that it always has to be (although frankly I think that combinations such as dexterity + occult are absurd).

Werewolf: the Apocalypse
Garou start with 100 experience points and three lupine Gifts. One additional gift may be bought for fourteen points. Select breed, auspice, tribe, pack and totem normally. Renown and rank are handled per the WtA rules, as are the different shapes and their ability modifiers.
If a rage roll is called for, the garou frenzies on a roll of 15+, and enters a wyrm frenzy on a roll of 18+. Stepping sideways requires a roll of 9+ on gnosis, and shapeshifting a roll of 12+ on endurance plus primal urge. Higher rolls on either increase the speed of the action.

Mage: the Ascension
Magi start with 250 experience points, and one rank in their traditional sphere (if any). Spheres cost fourteen points per rank for a traditional sphere, sixteen otherwise.


Conversion table
..... DotsAttribute rankAbility rank
Strength Strength 1 2 1
Dexterity Agility, Dexterity, Reflex 2 4 3
Stamina Endurance 3 6 4
Charisma Charisma 4 7 5
Manipulation Persuasion 5 8 6
Appearance (charisma) 6 9 7
Perception Perception 7 10 8
Intelligence Knowledge 8 11 9
Wits Intelligence 9 12 10

SkillBased on..... SkillBased on..... SkillBased on
Acting Charisma Etiquette Knowledge Melee Agility
Alertness Perception Expression Persuasion Music Dexterity
Animal Ken Charisma Firearms Perception Occult Knowledge
Athletics Agility Instruction Intelligence Performance Dexterity
Awareness Empathy Intimidation Charisma Politics Persuasion
Brawl Agility Intuition Empathy Primal Urge Endurance
Computer Intelligence Investigate Perception Repair Intelligence
Cosmology Knowledge Law Knowledge Research Intelligence
Culture Knowledge Leadership Persuasion Rituals Knowledge
Do Endurance Linguistics Knowledge Science Intelligence
Dodge Reflex Lore Knowledge Stealth Agility
Drive Perception Medicine Knowledge Streetwise Intelligence
Empathy (attribute) Meditation Endurance Subterfuge Persuasion
Enigmas Knowledge Survival Intelligence Technology Intelligence

Character sheets World of Darkness Simplex