SharePoint 2013 Features
http://msdn.microsoft.com/en-us/library/jj163091(v=office.15).aspx This page contains a huge amount of information on various different dev related topics. My personal highlights are Cloud App Model REST endpoints New client and server APIs Remote Event Receivers Workflow 4.0 Managed Navigation Cross-Site Publishing EDiscovery and many more Office 365 also availabe with free version.