You aren't going to be getting your hands on Android L for a while – the latest info suggests it won't be around until autumn (though a dev preview version is available now, that's a tricky thing to install and use). One of its features is floating notifications, and you can get a taster for the kind of thing that might be on offer by installing Heads Up! – notifications. As long as you are running Android 4.3 or higher you can install this app now.
Heads Up! - notifications pops up floating notifications on top of whatever you are doing. The key advantage of this is that you'll always know what you need to. You can select the apps that work with Heads Up so that you aren't overloaded with too much information.
The notifications themselves can be dismissed with a simple swipe, and a double tap on a notification opens the app with which it is associated.
Product: Heads Up! - notifications