The source is at
It is designed to interoperate with Caja: If cajita.js is also loaded, E code can call Cajita-tamed objects; also, the output of the compiler should be within the Cajita subset (I have not tested this). However, Cajita code can create objects which violate E sameness invariants.
It is as yet quite incomplete; especially, the compiler does not implement all of Kernel-E, and generates inefficient and verbose code.
Out-of-date demo XXX broken link
It supports converting an Updoc document, or a HTML document with embedded Updoc, into a HTML document such that the tests are executed. A (stale) example.
Not-yet-executed tests have dashed bars to the left, successful tests have light gray bars, and unsuccessful tests have red bars and show the expected and actual values (which are not differentiated except by color; this is to be fixed).
As this particular Updoc example was borrowed from E-on-CL, many of the tests fail because they are specific to E-on-CL in some way. Many other tests fail because in the demonstrated version there was no printing subsystem yet, so everything uses JS .toString() and thus the wrong syntax.