There is currently a Kickstarter campaign running for a 3" folding camp stove called the Firebox Nano.  It is a wood burning/multi-fuel stove where its stainless steel construction folds flat to .25". The creator is hoping to raise $8,200 to go into production for this little stove that can bring two cups of water to a boil in under five minutes. It looks like the campaign has successfully surpassed their goal, but you can still donate. Find out more about the Firbox Nano and the 5" Folding Firebox on their website and stay up to date on news by following them on Facebook.