I started Narwhal (a JavaScript standard library: http://narwhaljs.org) and Jack (a WSGI/Rack-like web server interface: http://jackjs.org) earlier this year with the intention of bringing JavaScript up to par with Ruby, Python, etc.
There are other nice SSJS products, but they're all very monolithic and self-contained (in a bad way). I'm hoping Narwhal will be more modular and open, like we have with most other languages.
While Rhino is currently the most complete Narwhal platform (mostly due to the ease of prototyping in it) We've also started working on V8 (github.com/tlrobinson/narwhal-v8/) and JavaScriptCore (github.com/tlrobinson/narwhal-jsc) support. They're still very incomplete but it's a start.
For example see Flapjax (http://www.flapjax-lang.org)