These are fairly simple to build, super light and essentially free. Uses an inexpensive fuel (alcohol) that doesn't need special canisters.
On the downside, they use a less efficient fuel and on longer trips the weight of extra fuel makes other stoves and fuels a better choice. And they only have one setting which is full power. I've seen attempts at simmer rings but haven't tried any of those.
It's a simple clone of Trangia alcohol stoves.
Still it's a fun project.
Here's one of many how-tos on the topic of an alcohol stove from beverage cans.
alcoholstove.com
We built a bunch of these as a boy scout project in the early spring then used them on an overnight hike in the summer.