Android (4.3 and above): Not every app's updates deserve your immediate attention. For those select apps you want to keep an eye on, Notify! puts their notifications on your home or lock screen.
It's very simlar to Dashclock, and while it isn't quite as nice-looking, Notify! works with every app on your Android device -- no need to download any extensions. Set up the layout you want, choose the look and format of the clock, and then select which apps you want to receive notifications from. The widget then just needs to be added to your home or lock screen and you're good to go.
The notification provides a complete preview, like your Whatsapp chats or the contents of a received email. Tap any and it will open the app -- this also works on the lock screen, which can lead to some accidental unlocks.
Notify! is free and doesn't have any ads, and (according to the developer) never will. For more layout and customisation options, you can pick up Notify! Pro through an in-app purchase.