Classes of Software
How an open source platform differs from a cloud service, a static site and a custom-built catalog.
Extension Ecosystems
How to tell core configuration from someone else's module, check the maintainer and compatibility, and read the plugin list of a live portal.
CKAN: Core and Extensions
What CKAN does by itself, what capabilities extensions add, and how to assemble a portal from them for a specific task.
Platform Profiles
What a platform does by itself, what an extension provides, which release to take and whom each platform suits.