Mozilla Servo alpha will be released in June
To echo what Paul said, this will not be a browser you will want to use as a replacement for all your day-to-day browsing. If you try to, you won't end up happy.Web compatibility is a long road, and it's crucial for us to be able to know what missing functionality is most important and the places where we need to focus on performance the most. The purpose of the package is to help us find and prioritize bugs and missing features. We want to know which sites are the most broken (and, even more importantly, which missing features are breaking those sites). From the Web developer side, we also want early feedback on use cases that may be slow today, so that the browser engine can eventually become a great experience for everyone.