A common application of HHO is in torches for the processing of refractory materials. Many forms of HHO lamps are available such as limelights which are used in the heating of lime. HHO does have an explosive nature and hence limelight lamps have largely been replaced by electric lighting.
A recent application of HHO is in running the cars on water. Several manuals are available online which provide precise instructions on how you can make your own HHO kits so as to install them into your car or truck. In context of cars, HHO is also referred to as Brown gas.
Water is usually stored under the hood of the car and it is ignited by the spark from the battery of the car. This starts the electrolysis of water as a result of which it is converted into HHO or Brown gas. The engine vacuum sucks this gas into the intake manifold, once it has been introduced into the airflow. It is this Brown gas, which when mixed with gasoline provides a better gas mileage.
Making your own HHO kits is really simple and does not require any extensive knowledge of your car or the chemistry involved behind its production.