Three years ago today, Google launched Duo, the video calling app and service it teased a few months earlier during I/O 2016. Along with Allo, Duo brought about a shift in Google's messaging and communication strategy. It spelled the beginning of the end for Hangouts and the switch to a more simplistic approach that didn't pan out well for Allo. Duo, on the other hand, is still advancing. It may not have completely revolutionized video calling, like Google had hoped, but that doesn't mean it isn't a success.

Since its inception, the idea behind Duo was to shed email addresses and usernames, and simply allow you to video call any person whose number you have. That reliance may have deterred several of you from using it and created a few limitations, but the Duo team has slowly knocked them down over the years. The service now has a web client and is no longer tied to one device, making it more accessible and useful for people with multiple phones and tablets — including iPads.

It also added audio-only calls, group calls for up to eight people, the option to leave video and audio messages to your contacts, and now has hooks to the Contacts, Phone, and Messages apps. But it's not just about adding features, Duo has also tried to make its calls more mobile and data-friendly. At launch, the service's ability to keep a call going regardless of connection strength and type was one of the features that most impressed me about it, and it still does. It's the most reliable app I've used for voice and video calls, and also one of the simplest. I barely, if ever, need to help my parents and in-laws figure something out with Duo, which wasn't the case when we used Skype.

Unlike Allo, Duo has received Google's wider support almost since launch. In December of 2016, it replaced Hangouts in the Google Apps package and became a mandatory install (like the Play Store, YouTube, and Chrome) for any Android device manufacturer. That helps explain the 1 billion install number that the app has reached on the Play Store. Duo was also integrated with Assistant on phones, Home speakers, and Smart Displays, helping expand its usefulness and reach.

But perhaps the biggest attestation to Duo's "success," regardless of how loosely you define that term, is that it's still standing, while many of Google's other communication efforts failed in fewer than three years. Given the company's tendency to shut down anything that doesn't work, that's a remarkable feat.

So happy birthday, Duo! May you keep on defying the odds and live to see a fourth candle on your cake and many more.