Microsoft says there are now more than 17,000 apps available on Windows Phone Marketplace. While the growth is certainly great for a new mobile OS, the software giant is still way behind Android and iOS. Access to apps will soon be expanded by launching Windows Phone Marketplace in new countries. That's not enough though, and the company knows it, so with the next release of Windows Phone it will launch a Web-based Windows Phone Marketplace.

The Web version of Marketplace will launch later this year and will serve as another way users can discover Windows Phone apps and games. Windows Phone developers meanwhile will get additional visibility for their creations with no extra work on their part. Here's a screenshot of what it will look like:

Just like on a Windows phone, you will be able to browse the full catalog, view screenshots, read application details and reviews, as well as choose from all of the supported languages for that app. The Web version of Marketplace will also have more placement areas to give featured apps extra exposure.

The best part is that the Web Marketplace will let developers promote their apps among friends, family, partners, and social networks. You'll be able to share your favorite apps by embedding a link in emails and articles, as well as make a recommendation through Facebook or Twitter. Purchases will be charged against the credit card linked to your existing Windows Live ID (or you can opt to assign a new credit card). Apps will be automatically downloaded over-the-air to your Windows Phone, or can be optionally installed later.

Web Marketplace will also be able to maintain your download history to make it easier to reinstall apps (when changing phones, for example). Parental Controls will let parents determine which apps their kids access based on ratings, or even stop their kids from downloading paid apps.

Earlier this week, Microsoft unveiled Windows Phone 7.1 (codenamed Mango), which the company says will include over 500 new features. Windows Phone 7.1 will be available for free to current Windows Phone customers and is scheduled to ship on new phones beginning this fall. We can expect the Web Marketplace around the same time.