Beyond the mountains that separate civilization from the wilderness, beyond the mists of the north, lay Forbidden Lands, once called the Ravenland—the promised lands of human settlers who once displaced elves, dwarves, goblins, and halflings. Now strange creatures dwell in those valleys, strange creatures that should not be, for that land is cursed. A human mage, Zygofer, long ago made it so; when confronted by an army of orcs, he summoned demons for their infernal aid. Zygofer and his daughter Therania came to rule the Ravenland, but the demons took their price from the old sorcerer and even the land itself.
For hundreds of years, a demonic mist descended over the Forbidden Lands, keeping its denizens close to their own hearths. The tiny communities that had managed to survive war, famine, and demons became tiny, isolated motes of settled life in the vast wilderness filled with monstrous beings.
You were born in this Forbidden Land, a child of one of these small villages. You came to your profession early in life, as all must do in small self-sufficient communities. But things are changing; over the last several years, the mists have come more-and-more infrequently. It might be safe to travel again, perhaps to trade, perhaps to adventure. Perhaps to find glory beyond your little village.
While I would argue that Forbidden Lands isn’t really an OSR game, this video gives a great overview of the system and the Player’s Handbook.