One of the advantages of an open sourced project such as this is that all the tools and progress are available online, along with the source code. The official site explains a bit more about how it works:
The app is released under a GNU General Public License. Both the app and the source code are free for you to download and use in any way you want. Of course we’d greatly appreciate your help in making WordPress for Windows Phone even better, so if you know your way around the code, or if you just have some good suggestions for the app, you’re more than welcome to contribute to the project.