Dabbing is a relatively recent innovation, but how fucked up it gets you is timeless. Dab rigs are similar to bongs in that they both utilize water filtration, but a rig has several distinct features that make it unique for dabbing.
The first is the recycler function, which is almost entirely exclusive to dab rigs. This means that the rig has two chambers through which the water within alternates, allowing the smoke and vapor to be constantly cooled by water.
Oftentimes on dab rigs you will not find as many intricate or overly complicated percolation systems. This is because more percolation means more filtration-- which is not ideal with dabbing, because it diminishes the very delicate flavor profile. The other reason dab rigs sometimes do not contain a lot of percolation systems is because it simply makes the rig larger. A smaller rig is ideal because, again, you want to preserve the flavor profile as much as possible-- and the larger the rig, the staler the vapor.