Torsen, mechanical, and helical are all terms that mean the same thing. Yes, there are subtle differences between manufacturers, but it's easier to say they are all the same.
My apologies to those of you that know more about differentials than I. This FAQ, like all of mine, are not the end all/be all of information, merely a jumping off point. One day I'll go through this and update it. While the information posted is not, nor is it intended to be 1000% accurate, I hope it stands as a good base. I could argue until I'm blue in the face about many of the points brought up here, but this is a BASIC post, not advanced. Want advanced? Call some Pat at Rocket Rally, or GEMS, or Franz Diebold, or people like that.
Don't like my FAQ? I challenge you to write one better.