Windows 8 Windows 8 app files

[Marios]

Can i download app files from other sites and microsoft app store for modern metro windows 8 OS without installing it directly from Windows app store before i install em? In what extension are they?

 

[patcooke]

Programs to install applications for running under Windows may be either .exe (executable files) or .msi (Windows Installer, previously called Microsoft Installer - hence MSI).

 

[Trouble]

Can i download app files from other sites and microsoft app store for modern metro windows 8 OS

Since you seem to be talking about modern apps, which I believe since Windows 8.1 and the rush to the whole "Universal Apps" project, are sporting the new .appx file extension.
I was just reading an article from HTG about side loading them, (something that has been available on Windows 8 phones for a while).
It seems like a huge amount of hoops to jump through, just to be able to do it but you can have a look here if it's something that interests you.
http://www.howtogeek.com/129535/how-to-sideload-modern-apps-on-windows-8/