During its keynote at this year's Google I/O developers conference the company announced Duo, a simple video calling app for iOS and Android.

It is designed to take on Apple's FaceTime and Microsoft's Skype by making the system as easy as possible.

As well as featuring end-to-end encryption, Duo will work on even slow, low bandwidth internet connections. It also sports an innovative new feature Google is calling Knock Knock.

This enables Duo to show live previews before a call has even been answered. That way users can see what the caller is up to before they pick up.

Not only does this help conference style calls, to give the recipient an idea of whether they need to answer if they are already busy, it can help start the conversation with family members immediately.

Google has ensured that the technology is super quick and that there is no lag before picking up a call.

We will test it when it's officially launched, but it certainly sounds interesting in comparison to rivals.

Google Duo will be available on Android and iOS "this summer", as will Google Allo, the company's messaging app rival to WhatsApp and Messenger.