The open source movement defies economic logic if you just superficially glance at it: people give away freely their ideas, their efforts and potential profits for the public good. Many software packages or operating systems, often superior to their commercial counterparts were devised this way. Beer is now also open source.
That does not mean beer is free. Rather, you can now brew beer using a recipe that is published under a Creative Commons (Attribution-ShareAlike 2.5) license by Free Beer. This means you are allowed to sell and make a profit from this recipe, and are even allowed to create derivative recipes.
This project started in Denmark. Why do they do it? The site is silent on this, but I have no doubt they just find it useful, so why not?
PS: And speaking of having a good time, here is an original way to blow birthday cake candles.