What is this weapon spotted at an airshow in South Africa?
@mins got this one right. It's a British Tigercat short range surface to air missiles launcher system. The cones are protective weather covers for the missiles which are removed prior to launch.

As to the 'buckets and chains' I'd venture a guess that they are a device to deflect and dissipate the rocket blast during launch but I am not totally sure. But they can be seen on YouTube (at 0:07 and 0:39).

From YouTube, on the right the blast being deflected up/down.