Open Adventure (beta stage) (2014)

website blurb:
Open Adventure is a full-featured tabletop adventure game that offers out-of-box support for medieval fantasy and science-fiction expeditions. In Open Adventure, you play as a heroic or villainous figure free to explore the perilous world created by the all-mighty Game Master. Along your adventure you'll battle ferocious enemies, solve complex puzzles and navigate labyrinthine mazes, and much more!

If your character is smart enough and strong enough, they'll discover treasure and wealth beyond imagination! However, the journey will not be an easy one and is not for the faint of heart. Death will come easy to those who do not think.

Thus warned, shall ye enter?

from How You Can Help:
In Open Adventure, people such as yourself help design, develop and discuss the rules of the game in an effort to bring back the spirit of fantasy and science-fiction gaming from the 1970's and 1980's. Because Open Adventure is open source, anyone is free to download, change and share the rules. Even better, Open Adventure is a living game that is always evolving to newer, better ways of play while never forgetting it's roots. You can help shape OA's future by offering your ideas, home-made rules or artistic passions.

These rules are available as a free download from the game website, see rpg level entry for link.