Simplified Design
A popular way to simplify the design of complex systems is to use queues and asynchronous processing. Using such a design, you'd have queues set up to handle the different events that transpire in your system. Instead of methods being called directly, objects are created and placed in queues where they will be handled. At the other end of these queues are server programs with multiple threads that are set up to "listen" for messages coming in to these queues. The advantage of this type of simplified design is that it provides for reliable, robust, and extendable systems.