Helma is one of the few Javascript server-side web frameworks, and it's next generation version runs right out-of-the-box on Google appengine. I followed the tutorial and easily got my own Helma NG demo running on appengine. Because Helma NG is a complete rewrite of standard Helma (which doesn't run on appengine), it is very simple, no persistence yet, mostly just request wrapping and routing and a simple template engine (no template inheritance and other fancy feature you find e.g. in django). If this is all one needs then Helma NG on appengine is now probably the easiest way to run javascript at client and server side. So let's hope that those who need a bit more, will contribute to Helma NG development to make it competitive with PHP, django and RubyOnRails, or come up with a new framework (RhinoOnRails ???).And for those who need less than Helma NG, this article might be helpful.
Update: I was wrong about template inheritance, Helma NG does support it, via the "extends" tag. And the development branch has now also appengine persistence support (demo).
