The code behind Google's Chrome browser has always been open source—it's known as the Chromium project. The Android port has thus far been more locked down, but that changes today with a big commit from the development team. Chrome for Android is now almost entirely open source, and that could mean some cool new browsers are on the way.
On the desktop side, there are a bunch of browsers that are based on Chromium, for example Flock, Opera, and Yandex. The code to roll your own Chromium on Android wasn't readily available before, meaning Android developers had to start from the desktop code. It was possible to get Chromium browsers working on Android (Opera does it), but it should be much easier now.
Developers interested in creating a mobile version of Chromium can build from the chrome_public_apk target. It should look and work mostly like Chrome, but codec support will be a little different (because licensing), and some of the proprietary Google features won't be there. Still, browsers could be more awesome very soon.