With virtual reality and augmented reality becoming more and more popular, it can be easy to look toward the future of technology. But what if the answer is a little simpler?

Google Cardboard, a cardboard cutout that allows users to mount their phone right in front of their eyes for a virtual reality headset, has now shipped 500,000 units.

"It's this same spirit that inspired our team to turn a smartphone, and some cardboard, into a virtual reality (VR) viewer earlier this year," said the company in a statement. "Suddenly, exploring the Palace of Versailles was as easy as opening an app. And the response was kind of delightful."

Google released Google Cardboard shortly after Facebook bought Oculus VR, a company that focuses specifically on virtual reality, for a whopping $2 billion. In fact, many suggest that Cardboard was something of a joke, poking fun at the fact that Google can build a virtual reality device without having to spend $2 billion.

To celebrate the success that Google has had with Cardboard, the company is releasing new specifications. Not only that, but it has also grouped Cardboard-compatible apps into their own category on the Google Play Store, allowing users to view them and launch them straight from their viewer.

A number of other companies have also launched their own Cardboard-inspired products. Google is embracing this DIY nature, and the new specifications are for anyone who wants to build the viewer for themselves, from mass-producers to one-time builders.

There are a total of four manufacturers that currently are selling Cardboard using Google's specifications, for between $15 and $35, including DODOcase, and I Am Cardboard, which sells the Eva with a near-field communication tag to be able to launch apps. Another company, called Unofficial Cardboard, says that it has sold 50,000 units and that number is growing.

The Play Store currently has more than 2 dozen apps for Cardboard, including a number of games and tours of locations. While most of the apps available for Cardboard are Android apps, there are a few Cardboard-compatible iPhone apps available on Apple's App Store.

Google has also launched a "Cardboard SDK" for both Android and Unity which is aimed at helping developers to easily create Cardboard apps and resolve issues such as "lens distortion correction, head tracking and side-by-side rendering." The SDK makes it easy to adapt an existing Unity 3D application to VR and make an app that can easily switch in and out of VR mode.

Google isn't ending its virtual reality efforts with Cardboard, however.

"The growth of mobile, and the acceleration of open platforms like Android make it an especially exciting time for VR," continued the company. "There are more devices, and more enthusiastic developers, than ever before, and we can't wait to see what's next! We're also working on a few projects ourselves, so if you're passionate about VR, you should know we're hiring."