Knock Knock! Who's there? Duo. Duo who? Du-o know that Google's video calling app has just surpassed 500 million installs on the Play Store? We need to take a few minutes to celebrate this milestone.

But before we get started, here's a little disclaimer: Duo is now part of the Google GMS pre-installed apps on Android devices — it replaced Hangouts almost two years ago — so it didn't achieve that feat by itself, but it was helped along the way by being installed out of the box on all new devices.

Still, 500 million installs is an important milestone for an app that was still at 100 million eleven months ago, and one we should appreciate for a bit. Duo is quite possibly one of the easiest video calling applications I have used in the last few years. Its video quality and audio fallback were essential factors in my husband and my decision to instantly ditch Skype and WhatsApp's video calls and switch over to Duo. Its simplicity and reliance on phone numbers instead of creating accounts and passwords were also the reasons we asked my parents and in-laws to use it so we can talk to them. To this day, I use Duo several times a week to chat with them while I'm cooking dinner at night. It has helped us stay in touch in a very communal way.

And Duo is frequently evolving. It added audio-only calls, integrated with your call history and messenger/contacts, and gave you the option to leave a video message if the person doesn't pick up. Recently, it also started implementing screen sharing and Google account linking, though both of these don't seem fully functional yet. Good things are on the horizon for Duo, and probably even more installs, huzza!