The browsable source code is here. Use the table of contents on the left to navigate. Most components are under src. An un-webified version is available from downloads.
has everything that doesn't fit anywhere else: dependencies, makefiles, generation scripts, XML configuration files, files for the web site. conf/package is where the components are packaged into usable images.
is where documentation files reside
has include files
has some sample programs and components that might either be educative or are included into documentation web pages.
has most of the actual system. src/base is the operating system core. src/web are the web service components (that are still under development). Other components are grouped under other subdirectories.
has programs for testing the system.
tools/