Businesses are unlikely to use the store for custom apps, though there are several alternatives. Visual Studio builds Windows 8 apps into packages with an .appx extension, and there is a PowerShell command, add-appxpackage, which will install an appx package. This is called sideloading, and can be used at runtime, or to build a Windows image. However, there are certain requirements that have to be satisfied before sideloading will work. It must be signed with a trusted certificate and Enterprise editions, or Server 2012, need only be joined to a Windows domain and have sideloading enabled in Group Policy – Microsoft’s system for configuring Windows centrally. Other editions of Windows 8 (including Professional) will not work for sideloading unless a special product activation key is used.