Our code is kept in git. You can check it out like this:
git clone https://git-wip-us.apache.org/repos/asf/kafka.git kafka
Information on contributing patches can be found here.
Official releases are available here.
The source code for the web site and documentation is kept here. We think documentation is a core part of the project and welcome any improvements, suggestions, or clarifications.
To setup IDEs for development, following this guide on the wiki.