Recently, I upgraded the Granite State (NH) SharePoint Users Group's website from WSS 3 (MOSS 2007 generation) to SharePoint Foundation 2013. The upgrade itself went as well as a 2007 to 2010 to 2013 upgrade could go, in general.
The only real "problem" I ran into was the Windows Phone app I wrote for the group years ago. It was coming up with a 401 error trying to grab content from lists.asmx.
I spent some time digging in the dirt, trying to resolve the 401, and hit a few common settings known to have an impact, but no good.
Rather than struggle with it in my not so copious amounts of spare time, I decided to trash the old app, and build a new one with AppStudio.
The app loads content from the #NHSPUG web site (http://granitestatesharepoint.org), mostly via RSS feeds. I put a little extra effort into this. Using AppStudio (http://appstudio.windows.com), I found a couple hours... after that, I had not only a much prettier v3 of the Windows Phone app, but a Windows 8.1 (tablet style) publishing package as well.
One thing that caught me off guard though... the Gotcha:
The Windows 8.1 edition of the app wouldn't load the content from the users group website.
With some debugging, I found that attempts to load the content were coming up with "Unable to connect to the remote server. hresult= -2146233088".
Turns out the error had to do with the fact that I had not enabled Capability "Private Networks (Client & Server" in the Package.appxmanifest. Ironically, the app works fine anywhere except where I was trying to test it: on the same network as the content source server. So, to be fair, this is an environmental/configuration issue, not AppStudio, but it was worth mentioning, since my original assumption led me down that path. Maybe this will help someone else.
Oh... Here's the Windows Phone app:
And here's the Windows 8.1 (tablet style) app:
And here's my moment of shame recording the incident and solution in the forums: