The Odin Project is a free open source learning resource created in 2013 by Erik Trautman. It's a structured web development learning programme focussed on Ruby-on-Rails and associated web technologies.
The Odin Project is innovative and has undoubtedly driven the development of a number of structured free web development learning resource. I found the resources to be of a consistently high quality. Learning is supported by an active community of learners participating through the gitter.im chat and networking platform.
The emphasis on learning the back-end first seems counter-intuitive. While this is a good way to develop your understanding of the full-stack, many (myself included) will find the long study period before you actually get to produce a good quality web application a disincentive.
While I think the Odin Project has a lot of value, I believe that the time it takes to get from a beginner level to being a competent web developer makes it not the best choice as a first step. For developers such as myself who intend to focus on front-end development - I believe that this is not the resource for you, or at least not the first one you should be dedicating your time to. It is however a resource that I will be revisiting in the future to build my back-end skills.
For more information, visit the Odin Project website.