One of the first things that came to my mind, even before Brazilian Jiujitsu, was Harimau Pencak Silat. It can be seen in this video:
The Harimau ("Black Triangle") style of Silat is modeled on the movements of the tiger and has a specialization in ground fighting. One of its primary strategies is to take someone to the ground and finish them off there with bone breaks, submissions, and strikes. It is also taught defensively, as in how to rapidly recover from falls to the ground when your opponent is either standing or is also on the ground with you.
Grappling in Harimau targets the opponent's legs as well as making heavy use of the practitioner's legs in many sneaky, off-angle ways. There are leg and arm bars. There are chokes. There are heel hooks. There are throws. There are leg scissors, single and double arm take-downs, lots of different kinds of sweeps, and other take-downs, often done from an inferior position. All kinds of interesting things done in a highly stylized manner.
I don't consider this form of ground fighting to be "superior" to Brazilian Jiujitsu's ground fighting system, but it certainly is interesting and worth looking into if you haven't already. The techniques in the Harimau style can be incorporated into BJJ, MMA, and other arts on a piece by piece basis.
That video was just a small sample of what's in the style. You should do a search for other videos on Harimau to get a better understanding of it.
Hope that helps.