Core Resource Libraries
The core resource libraries are concise, role-based views of the Force.com platform. The documents in the libraries don't have to be read in a particular order, and provide a good introduction to a logical slice of the platform.
These libraries are continually being refined and extended—check back soon for new resources.
Developer Core Library
The Developer Core Resource Library is a set of resources covering all the fundamental aspects of the Force.com platform and its various components, aimed at a developer audience.
These resources will get you up to speed on the platform, providing all the necessary background and pointers to get you started developing applications and solutions quickly and efficiently.
The resources look at the logic, database, user interface, integration and security layers.
Architect Core Library
The Architect Core Resource Library is a set of resources covering all the fundamental aspects of the Force.com platform.
These resources serve two audiences: those who want to understand how the Force.com platform and architecture can be used to fit into and extend their existing infrastructure and security frameworks, and those who want to understand how to architect applications on Force.com for commercial purposes.