open systems

Open Systems: How would you define? What are your favorite examples? Are they always appropriate?

Hey gang,

I've been doing a bit of thinking about "open systems". This is not the same thing (though related to) open source. In fact, I've been thinking of how IxDA itself exemplifies a lot of the properties of an open system.

I'm curious what people think about open systems: how do you define them for yourself and what are the examples you point to? What are examples when they are not appropriate?