Uncle Jimbo's Get Mediaeval
|"Downward and onward!"|
Campaign Model: Amnesia
In narrative terms, the DM can easily describe the players' surroundings physically without giving them information that their characters wouldn't know. It's generally fine for them to guess what the DM described and react appropriately, since the whole point of most such campaigns is for the characters to deal with a past they've lived through but don't consciously remember (and to run into surprises that invalidate their assumptions).
The following mechanics combine what my DM did for a previous campaign, some conversions and some thoughts of my own:
Each character starts with a race, ability scores and the hit points and healing surges of a wizard.
A character can claim a weapon, armour or implement that he finds and choose to be proficient with it. After a short rest, he recovers his memory of a class that is proficient with that item and/or one feat that makes him proficient with it. For example, if the item is a superior weapon, he may instead take the Weapon Proficiency feat. If the item is plate armour, he may instead choose any class trained with scale armour and take the Armor Proficiency (Plate) feat. If the item is a ritual book, he may instead take the Ritual Caster feat. He might choose to take a multiclass feat that grants the ability to use the item.
When a player chooses a class, he gains class benefits that are automatic (proficiencies, defences, hit points, healing surges and class features that all members of the class get) and makes any decisions related to his claimed item (such as Fighter Weapon Talent - he's not required to take the class option that's optimal for the item) but doesn't gain powers, skills or make any other decisions.
When a character is required to make a skill check, the player can choose to be trained in that skill if it's on his class skill list, or to take a feat that makes him trained in that skill (Skill Training or a multiclass feat). He can do so even if he rolled an earlier check against that skill as untrained. If he doesn't have a class, after a short rest, he gains a class that has that skill on its skill list. However, if he chose to take a feat, he doesn't get a class and should be careful later not to take a class that has the skill on its class skill list (the character may retrain after an extended rest if a player paints himself into a corner on this).
A character who has a class can choose any of its first-level powers in combat and has that power thereafter. A character who doesn't have a class can only make basic weapon attacks and use other basic actions.
A player who has gained all the powers, feats or skills he's entitled to may not choose any more.
After an extended rest, the DM might require any character to resolve by retraining any discrepancies in the abilities he's picked. If the DM intends to run the campaign at higher than first level, each character who has a class also gains a level after an extended rest and can start to choose powers of his new level, until the party reaches the desired level.