The Basslet is technically a tactile transducer or a bass-shaker. So it is basically a portable sub-woofer that runs on batteries. But it can reproduce frequencies as low as 10Hz which is far lower than most mainstream sub-woofers. It can also do 6 hours on the go. It also makes no sound at all, just pure unadulterated bass waves.
One downside is that it is not fully cordless but as the first iteration of a ground-breaking product, that is pardonable.