What RPG systems are there for a traditional Call of Cthulhu adventure (e.g. a basic premise of being investigators in 20th century/modern timeframe within the Lovecraft Mythos)? I know that there is the Chaosium Call of Cthulhu system, which I understand is the grandaddy of them all, and I have heard that a d20 version was made. Which others are there? Also, are they in print?
Also, could I have a bit of information about what the basic differences are (e.g. main mechanic, how it tries to capture the feel of the setting) to better help me decide which one I'd like to use?
I also realize that there are a bunch of other spinoff games based on the Cthulhu mythos (e.g. The Laundry and CthulhuTech) but I'm not interested in those at the moment. Also, I'm not looking for general horror RPGs, but rather ones that are specifically designed to be set in the Cthulhu Mythos.