Caja will be open source, under the Apache License. We’re still debating whether we will drop our existing code for this as a starting point, or whether we want to take a different approach, but in any case, there’s plenty to be done.
Although the site has been up for a while, I was reluctant to talk about it until there was some way for you to be involved. Now there is – we have a public mailing list. Come along, read the docs (particularly the Halloween version of the spec) and join in the discussions. I’m very excited about this project and the involvement of some world class capability experts, including Mark Miller (of E fame) who is a full-time member of the Caja development team.