Not only does VSTa have a deliciously consistent and simple
architecture, but the code is some of the best I have ever seen in
public-domain software. I am working on a port of xkernel so it can
have some networking other than ka9q.
This system borrowed heavily from the concepts of KeyKOS. It will
thankfully be released under the MIT public license rather than the GPL.
Some impressive performance numbers, but the code needs serious
clean-up. The most interesting feature to me is their DPF network