Google has launched Duo, a bare-bones video calling app that works across Android and iOS. Duo offers one-on-one video chat between smartphone users and is a direct competitor to Apple FaceTime.

Duo is the latest in Google's growing menagerie of communications apps, soon to be joined by Allo, an AI-assisted chat app based on the GSMA's Rich Communications Services (RCS). It too is a cross-platform service and both apps offer end-to-end encryption.

Unlike Google Hangouts, which also offers video chat, Duo doesn't need a Google account to use. Instead, smartphone users register with the app using their phone number, much like WhatsApp.

They can then place video calls to anyone in their contact list who also has the app installed, regardless of whether they have an Android smartphone or an iPhone.

Google places emphasis on Duo being stripped-back affair, ditching added frills and complexity in favour of a fast and reliable video calling service. You hit a button, you start the video call, and you talk – not a sticker or a filter in sight.

Google says the app manages "seamless" calls even on slow networks by dropping the video resolution when bandwidth is limited. Duo will also automatically switch to Wi-Fi when one is available if it will provide a better connection, without dropping the call.

A Knock Knock feature is also included, which lets you see live video of the caller before you answer a call. Reports suggest the feature only works on Android smartphones.

It's difficult to predict how much traction Duo will get when then are so many established players already on the market - such as Facebook - offering something similar. Bundling the app with future Android releases will guarantee it a large install base in its own market, but Google could face a hard time convincing FaceTime-loving iPhone users to sleep with the enemy.

Duo is being rolled out to Android and iOS starting today (16 August). You can check out Google's cringe-inducing promo trailer below.