IIS Express : Run a child web application in a virtual directory under a parent application

Like this: Edit your IIS Express config file at

"%userprofile%\My Documents\IISExpress\config\applicationhost.config"

Create a site which has two applications defined in it, e.g.

<site name="MyTopLevelAndChildWebAppsInOneSite" id="123" >
    <application path="/" applicationPool="Clr4IntegratedAppPool">
        <virtualDirectory path="/" physicalPath="C:\Users\me\Source\TopLevelWebApp" />
    </application>
    <application path="/Child" applicationPool="Clr4IntegratedAppPool">
        <virtualDirectory path="/" physicalPath="C:\Users\me\Source\ChildWebApp" />
    </application>
    <bindings>
        <binding protocol="http" bindingInformation="*:51234:localhost" />
    </bindings>
</site>

And then run the site, matching it on the siteid:

start "Woo!" "C:\Program Files (x86)\IIS Express\iisexpress.exe" /siteid:123

Browse to, and close, your web apps in the usual way from the IIS Express icon in the systray.

Optionally, experience the pain that is web.config inheritance. But try not to.