The GitHub repositories contain all components of the frameworks, the documentation, sample applications (i.e. the Sandbox), and further tools.
The code repository contains the core of the framework. In case you want to use it on your local environment, just do the following:
mkdir APF && cd APF git clone https://www.github.com/AdventurePHP/code .
Now, you can run your applications as you are used to for normal APF releases.
Please note the remarks on the structure of the repository under GIT Repository.