Dungeons and Dagon is a free RPG of adventure in the world of the Cthulhu Mythos.
RPG
New Crobuzon RPG Setting
I’m a big fan of the work of China Mieville. His stories are highly imaginative, and like nothing I have ever read before. Here’s an attempt by one fan to create an RPG background based on his New Crobuzon setting.
Hulks and Horrors RPG
Hulks and Horrors is an RPG about exploring the dark reaches of space for riches. It’s a pay-what-you-want product.
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Fantasy Fudge
Fudge is a free — and free to adapt — rules-light RPG that has been ported to a great many settings. At the link below, you’ll find FUDGE (Freeform Universal Donated Gaming Engine) Fantasy rules.
Free Elements LITE RPG
Free Elements LITE is a starter version of a more complex RPG where, according to the author:
This system utilizes the Elements TTRPG system, which is a freeform action system. You perform actions by describing what you want to do, and picking a skill to use. Based on that skill’s rank, check your multiplier table to see how many points it has. All checks require skill rolls from both parties to determine the success rate, regardless of what the target may be, you’ll engage in a battle of skill checks with it. If you don’t have the proper skill, you must perform an untrained skill check with it. Rate of success when performing an action determines the outcome of a battle, if successful enough the DM will allow you to describe the outcome, where if you’re within 9pts of each other’s checks the DM will describe what happens instead.