Unfortunately having Powerbullet's source code open doesn't help with
any long term development, because it makes heavy use of Microsoft's
MSHTML module. This is the layout and rendering engine used in IE and
many other interfaces in Windows. But all versions of Powerbullet,
including the Pro version are now free. The source code up to version
1.35 is available (the latest version 1.44 got lost in a web server
back-up stuff-up) to anyone who wants it, but not recommended for open
source development because of the MS Windows dependency. A similar
thing could be done using Firefox's Gecko rendering engine, however.