The source code of the Alfresco Repository (Community Edition) is available at the following GitHub project:
https://github.com/Alfresco/alfresco-community-repo
You can find all the software component developed by Alfresco looking at all the projects under the following GitHub account:
https://github.com/Alfresco
The source code of the Enterprise edition is available as Maven dependencies under authentication on the Alfresco Nexus instance:
https://maven.alfresco.com/nexus/
For example the source code of APS is available as a specific Maven dependency named activiti-bpm-suite:
https://maven.alfresco.com/nexus/#nexus-search;quick~activiti-bpm-suite
