According to a tweet image by Justin Angel who is former Microsoft program manager with access to the Windows Phone 7 Marketplace, Microsoft has already started to populated the yet unreleased Windows Phone 7 Marketplace with a couple of third party applications along with in house apps.
The images reveals that there are at least placeholders for a variety of games and productivity tools as well as Yelp and YouTube ( which is listed as a “Music Hub Add-On.”). It is unclear at this stage, If, not unlike Android WP 7 will have Adobe Flash 10. Nonetheless, having popular third-party applications would endear the Moblie OS to the users.