Which Javascript minifier (cruncher) does the same things that the one Google uses for its JS APIs?

Question

I am a Google Maps API (javascript) developer. I have noticed that Google uses a Javascript minifier that has the following features:

1. Shortens variables, prope

Answer 1

Google has now opened up the minifier they use along with some other internal javascript goodies.

It's all under the name "Closure Tools" and was announced earlier this month.