Jainja claims that all the major features of Java 1.5 specification is supported. A demo of Jainja JVM is available as a Chrome App. A Tetris game is hosted in appspot using this JVM and its quite impressive. Response of the application in the browser is sluggish. The project source is available and hosted at SourceForge.
This is an at building a JVM. This is more like a proof of concept (POC) and is not a full-fledged JVM. This is attractive in the sense, we can learn how and where to start for a similar project.