If you are not a developer but thinking of installing some apps to try that are not available from MarketPlace, you can now get access to them via ChevronWP7..
Tag: ChevronWP7
ChevronWP7 Bypass Marketplace to Load Apps to Windows Phone 7
Finally, some answers had been answered to Windows Phone 7 community to bypass Marketplace to install App. ChevronWP7 is touted to be able to allow users to install app minus Marketplace.