Announced at Microsoft's //build/ developer conference is a special "Summer Break" offer that sees the registration fee for the Windows Phone Dev Centre reduced from $99 to $19 for a limited time. In addition to attracting new developer to the platform, Microsoft will be hoping to encourage developers who have created, but not published, apps to formally release their apps to the public. 

For those creating free apps in their spare time, either to scratch an itch, or to get familiar with Microsoft's mobile platform, the $99 can sometimes be a barrier. We wouldn't expect to see any major apps arrive on Windows Phone as a result of the promotion, but it may encourage growth of the "long tail" of apps, something that will help Microsoft in the perception battle around the app gap.

From the Windows Phone Developer Blog:

Summer is a great time for vacations, having fun, and building apps. We want to help you make the most of all three, so for the next 60 days we’re offering a “Summer Break” on Dev Center registration with a $19 annual registration fee (normally $99 for individuals and companies). We know many of you have downloaded the SDK, have started building an app, and just haven’t had the time to finish and publish your creation. Now you have the opportunity to do so. If you could use a little help getting started, this week we published a refresh to our popular educational series – Windows Phone 8 Development for Absolute Beginners.