The FLOW3 package is composed of modules, each of them playing their own important part in the framework:

• The Object Manager is in charge of building, caching and combining objects. It is a lightweight Inverse-of-Control container with first-class support for Dependency Injection.
• The AOP Framework enables you to use the powerful techniques of Aspect Oriented Programming.
• The MVC Framework takes care of requests and responses and provides you with a powerful, easy-to use Model-View-Controller implementation.
• The Persistence Framework realizes a unique transparent persistence layer based on the principles of Domain-Driven Design, backed by our JSR-283 based content repository.
• The Validation module provides a validation and filtering framework with built-in rules as well as support for custom validation of any object.
• The Property module implements the concept of property editors and is used for setting and retrieving object properties.
• The Package Manager allows you to download, install, configure and uninstall packages and share new features with the FLOW3 community.
• The Resource Manager contains functions for providing, caching, securing and retrieving resources.
• The Signal Slot sub package provides an annotation based event system based on the Signal Slot design pattern.
• The Error module handles errors and exceptions and provides utility classes for this purpose.
• The Reflection API complements PHP's built-in reflection support by advanced annotation handling and metadata caching for speed.
• The Security Framework provides "touchless" security by enforcing security policies through AOP.

... and much more