I want to start another App or Program from my Windows Store App. For example my App is showing emails, so if someone clicks on such an email Outlook should open. Is this possible in an "App-Sandbox"?
It is not possible to just launch an arbitrary application, but with custom protocol activation you can launch an app that handles that protocol and if it is not installed - the OS will ask the user to install it. It means that if you can define a custom protocol in your app - you can launch it from another app with this protocol assuming no other app registers to handle it. An example of that is any XBOX Live app - if you check their manifest files - they all handle custom protocols.
If your specific question is about launching a specific app by name or location then no, this is not possible, but if you know a protocol handled by the app you want to launch - you can try using that - just bear in mind that there might be other apps that handle that protocol.
Short answer: no, it's not possible.
You can open files with their associated application but not spawn any arbitrary external process.
As @mitch-wheat pointed out, that's why it's called a sandbox.
Check out this sample
The sample is for Windows 8.1 but I think will work for Windows 8 as well.
来源：https://stackoverflow.com/questions/17969019/is-there-a-possibility-to-start-another-app-or-program-from-a-windows-8-store-ap