Back in 2010, we released the Open XML Package Editor for Visual Studio, a plugin which allowed users to open Office documents in Visual Studio and edit the OPC package content directly.
It's a great tool for anyone working on debugging or developing Office Open XML documents – since we shipped it it's had over 35,000 downloads, and I personally use it all the time.
Unfortunately, as is often the way with these things, it was developed in 2010 for Visual Studio 2010, and so you need to keep a copy of VS2010 around in order to use it. Well, I'm pleased to say that in the last few weeks we've rebuilt the project so that it now works in VS2012 and VS2013, supports Visio's new VSDX format and has a few other handy minor fixes and additions. And I'm especially pleased to announce that we've published the code as an open-source project, here on GitHub (under the Apache 2.0 license). So if you have a burning desire to get it working in VS2007, have at it!
If you just want to download the new version of the Package Editor, it's here on the Visual Studio gallery.