Protocol Activation: What Is It, What Apps Offer It, and How Can I use It in My Apps?
TL:DR
Protocol activation is a cool feature you can add to your Windows Store apps, and allows you to make your app more useful as well as more discoverable. For a video demonstration of how easy it is to add protocol activation to your app, skip to the end of the post. Otherwise, read on...
Helping Apps Collaborate
I've written in the past about a very useful feature of Windows called protocol activation (a feature that's not new...in fact, it's what allows an https:// link to open your default browser...but is particularly useful in the context of Windows Store apps), and how I've used this feature to add maps and directions to my Community Megaphone app (see below) without having to write any of the code for that functionality myself. Protocol activation allows both desktop and modern apps to register themselves as handlers for a given protocol or URL scheme. Some, like http: are well-known, and understood. Others may be custom schemes that are unique to the handling app.
In the case of the Maps app that comes with Windows 8, the custom schema for its bingmaps: protocol is well-documented, which is how I knew I could use it in the Community Megaphone app.