Strange Aeons is a commerical rules set, but if you already own it, you may be interested in these free modifications for playing in an 18th Century setting.
Arkham Express is a quick play adventure game set in the Lovecraft mythos. From the Board Game Geek description:
Arkham Express is a cooperative dice-based game designed by David Willems. Players are working together to gather clues, kill monsters, close gates and eventually defeat the Great Old One (Cthulhu).
Players will select characters, each with a unique special ability. During a player’s turn they will roll 5 dice with unique symbols on each side, after rolling they have the option of re-rolling 3 more times. If the “Monster” symbol is rolled on a die it is locked and cannot be re-rolled. If 3 Monster symbols appear a new gate opens and a monster appears in Arkham. The other sides of the dice include movement points, clue tokens (used to close gates), healing, and combat symbols (used when fighting the monsters guarding the gates). Each player must carefully choose how to use their symbols to move around and try to close and collect six gates. If six gates are open on the board the players automatically lose.. However if the players manage to close six gates Cthulhu awakens and players must try to defeat him with their remaining items and abilities.
For Cthulhu fans, here are some paper figures of an Elder Thing and Investigators.
Great Old Ones offer the rules for a two player card game where the goal is to reduce your opponent’s sanity to “0.” You need to make your own cards to play.
A few years ago, I bought a box of Pokethulhu miniatures — little figures that look like Pokemons crossed with Cthulhuian Horrors. I had no idea that there also was a role playing game to go with it. And it’s free! Pokethulhu RPG.