Brendan covers some really exciting announcements about the Tamarin project, which aims to:

implement a high-performance, open source implementation of the ECMAScript 4th edition (ES4) language specification. The Tamarin virtual machine will be used by Mozilla within SpiderMonkey, the core JavaScript engine embedded in Firefox®, and other products based on Mozilla technology. The code will continue to be used by Adobe as part of the ActionScript™ Virtual Machine within Adobe® Flash® Player.

Not only will Tamarin become the VM for JavaScript in FireFox, there's work being done on getting it working in IE, and also work to get IronPython and IronRuby to also map onto Tamarin. This is an interesting development as it appears that with Tamarin we have a solid VM, with JIT support, that will be widely available and embedded into many applications and that actually deigns to touch "C"-land. The nice part is that in theory Rhino could also be brought up to ES4 and then you'd have a language that was available in "C"-land and on the JVM, if that kind of thing is important to you.

That at least gets us half of the requirements for a 'real' language, which is technical depth on the language development side. The other half of the equation is going to be a broad set of libraries, which I am going to need if I am going to write server-side applications in Tamarin. Currently there isn't a lot there and it will be interesting to see if/when we have SWIG for Tamarin.

Update: A similar perspective on the need for libraries from Tom Insam, who wrote mod_js.