Interesting javascript projects you probably knew about before I did:

Appjet, an online server side Javascript application hoster has now made their software available for download - check it out http://appjet.com/download

Couchdb, a JSON/HTTP based distributed storage system (written in Erlang!) is now an Apache incubator project - http://incubator.apache.org/couchdb/

Helma is a Java based server side Javascript scripting environment and is at http://dev.helma.org

Persevere, similar to Couchdb but not quite, is at http://persevere.sitepen.com/

A list of server side Javascript projects is at http://en.wikipedia.org/wiki/Server-side_JavaScript

And, I'm still excited about Haxe - a compiler that targets the Neko VM, Javascript, PHP and Flash.