As far as I can tell, there are no commercially available tongue operated controllers currently on the market. This seems to be an important unmet need.

The most common competitive devices are mouth controlled joysticks. There are several models commercially available. I was very surprised that they all seem to be extremely expensive; especially when considering that many of their users have limited budgets. 

Two common models are the QuadJoy and the Jouse, both ringing in at well over a thousand dollars. The TetraMouse and QuadStick are less expensive, but still cost many hundreds of dollars each. 

While mouth controlled joysticks are in some ways similar to the BYTE, there are important differences. One differentiator is the type of muscles involved in using these devices. 

The lip, jaw and neck muscles involved in operating these joysticks tire much more quickly than the tongue (Think of the last time you had to hold a smile just a little too long for a slow photographer...). The tongue is very similar to the type of muscle comprising the heart, rendering it nearly tireless. 

Another advantage of a tongue controlled interface device has to do with the robust and direct connection of nerves from the tongue to the brainstem. Most people with spinal cord injuries, and many with otherwise paralyzing neurological diseases, can still move the tongue.

Several tongue operated controllers have been demonstrated, although mostly limited to one-off prototypes and academic research. A well known example comes out of Georgia Tech's Bionics Lab, the Tongue Drive System, using a magnetic tracking approach.  It requires the user to have their tongue pierced with a magnetic stud; for those with a strong stomach a paper detailing the procedure is available here. 

Aside from no piercing requirement, the BYTE has a major advantage over a magnetic tracking approach, especially for those with cerebral palsy - since it is pressure controlled, there is no need to accurately position the tongue within the mouth or to make small precise movements.