Alcohol stoves are perhaps the most lightweight backpacking stove solution available today. In addition to weighing mere ounces, they have become popular with backpackers in recent years because of the availability of denatured alcohol or HEET to use as fuel and the many items from which a stove can be improvised. Any heat resistant, small container, such as a soda can, tuna can, cat food tin (Fancy Feast are popular) or an old baked beans tin can be turned into a an alcohol stove. Patterns and ideas are widely available for download.
Disadvantages to alcohol stoves are that they usually only put out enough heat to boil water, are slower than canister stoves and can sometimes be dangerous if the user wrongly believes the stove is out (the flames are not always visible) and attempts to move it, spilling the burning fuel.