I think it's open source, and it's at the heart of the MeeGo 1.2 Harmattan security model. I don't know too much about it, but it locks the device down pretty good. For instance, you can't just recompile something and run it. You have to package and deploy it. Here's a good starting point if you're looking for something in-depth. My understanding is that some of the hooks are built into the kernel, but I don't know that anyone has successfully installed an aegis-free kernel yet.