Run Metro application on startup?

Simply,

Windows + R and run shell:AppsFolder

You will see all apps in this window. Create a shortcut to the desktop, then copy that shortcut to the startup folder available at shell:Startup or found at the following location:

%SystemDrive%\Users\{username}\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup

There are some tricky ways to start these Windows 8 applications, you need to find out its special name and since you cannot launch them with their executable (it only can be run from within Modern UI environment) but this is one way to start some of them.

To launch the calendar application:

%windir%\System32\cmd.exe /c start "" "wlcalendar:"

To launch the people application:

%windir%\System32\cmd.exe /c start "" "wlpeople:"

You can try them from the Win+R as it is launched using cmd.exe

Here a list of some of them I found:

%windir%\System32\cmd.exe /c start "" "xboxgames:"

Just look for their names in Windows registry:

HKCU\Software\Classes

Example:

HKCU\Software\Classes\wlpeople

If they contain their default value with data like the following:

URL:wlpeople

Try with that name with the command shown above.

And just make a shortcut and place it inside Startup folder

Win+R -> shell:startup -> intro

Some of the application cannot be found there, so this is the only method I know for the moment.

[UPDATE] And since those ":" <~ seems like calling a URL and its value contains URL: you can just use its name to launch them.

Example: (try it with Win+R just write its name and hit enter)

wlpeople:

ms-mail: for your mail client

The answer from vhanla (Nov 1, '12) has a problem: you're only launching the default application. For example, if I run mailto: then Outlook opens, not Mail.

In Windows 10, there's another way:

If you open the start menu and All Apps, you can normal click and drag (left click) a modern app, to create a shortcut. It doesn't work if you typed the name of the app into search, but it works if you browse to All Apps.