
Android L is now available to Nexus owners to download in beta, however, because of the fact that it's still in beta, it is a little buggy. There are a number of issues with the software in its current form. Luckily Koush has developed a solution to one of those problems.
The new notification system in Android L is nice, but it lacks a way to clear all notifications, and instead users have to clear them one by one. That solution has now been fixed. But not by Google.
Developer Koush has created the fix, an app that adds a Clear Notification button. It looks great, is simple, and works perfectly!
Source: +Koushik Dutta
Seams a little strange to talk about fixing things in a Developer Preview, there is not a released or finished product, This not a beta product, more like an pre-alpha product.