FlexyTrack is a free Blender extension available on the Blender Extensions platform.
Another similar addon is Damped Track Chain.
Although this addon does not perform any simulation, I have made it a part of the Bone Dynamics category. Instead of simulation/dynamics, the addon uses the Damped Track constrain to create automatic wiggly motion.
I’m personally not a huge fan of this technique since technically it’s a hack that relies on a cyclic dependency loop. But, I have to admit that it has a fairly stable, reliable behavior, and Blender riggers have been using it for quite a while with good results.
So while I won’t personally use it much, if you like the Damped Track trick for wiggly motion, this addon will save you some setup time!