I'm trying to understand the concepts behind DDD, but I find it hard to understand just by reading books as they tend to discuss the topic in a rather abstract way. I would like to see some good implementations of DDD in code, preferably in C#.
Are there any good examples of projects practicing DDD in the open source world?
Eric Evans and a Swedish consulting company have released a sample application based on the shipping example that Eric uses throughout the book. It's in Java, but the concepts are well documented on the project page.
http://dddsample.sourceforge.net/
However, be warned that DDD is more about the journey than the destination. Understand that the sample code you are looking took many forms before it became what you see now. You did not see the awkward models that were used initially and you're missing the steps taken to refactor the model based on insight gained along the way. While the building blocks are important in DDD, Eric belives they are over-emphasized, so take all samples with a grain of salt.