I understand that some weren't too thrilled with the new, official design for General Grievous (which you can see here).
First, hopeso009 developed this version. Dramatic pose, all TLG parts (except the cape of course). All in all, very nice.
This in turn inspired yoshix to create this. The additional parts give The General more size and menace. Granted, he's not likely to fit in the Starfighter, but when you need to bear down on a few Jedi, he's your man...er, droid.