The developers over at Jolt Online Gaming have released Legends of Zork to the general public. It's a free, browser-based, adventure game based on the world of Zork. You play as a Traveling Salesman, recently laid off from FrobozzCo. You start off in a clearing, where a white house has a boarded up door. From there, you can do what you like. Explore the world, fight other salesmen in PVP, or try out your Darkvision Goggles in the dark just try not to get eaten by a grue."
It's free in that you're given 30 Action Points each day, which are consumed by moving about and fighting. Their business model is that if you want more Action Points, you can purchase more.

http://games.slashdot.org/games/09/04/03/043201.shtml