I want to develop Document Manager application based on Alfresco. I am going to change there many things: user interface, language, may be some functions... But I don't know how to start, where I can get Alfresco source code, how can I rewrite codes with netBeans and how can I test my changes. This is my first serious project so I need any help. Where I can get Started ?!
A very popular way to get started is to work through my tutorials.
You don't need the source code, although it is available and helpful when you are troubleshooting or learning how something works. Instead of forking Alfresco you will write extensions that customize the platform. If you find yourself needing to compile Alfresco's source code, most likely you are doing something wrong.