When the folks behind “Hamilton” wanted to build an app for the smash musical quickly last year, they turned to a little-known mobile software framework called Flutter that Google quietly previewed just a few months earlier to help developers create user interfaces more easily.

Now, more developers will be able to use it. Today at the Mobile World Congress conference in Barcelona, the maker of the Android mobile operating software said it’s releasing the open-source Flutter into a wider beta test.

The purpose of Flutter is to give developers a faster way to create native mobile apps — in particular the user interfaces for the apps — which can take more time to create on individual iOS and Android app toolkits. Google’s pitching it for use with its Dart programming language, which it said is faster than the commonly used JavaScript and can compile source code for an app to native formats used in iOS and Android.

Seth Ladd, Google’s program manager for Flutter, said in an interview that the beta version is more stable and mature than the alpha version, with new features such as accessibility, localization, iPhone X and iOS 11 support, inline video and “hot reload,” which allows for updating of changes in a code emulator in under one second.

All this, Ladd said, has “accelerated the ability of teams to work faster.” He said there have already been millions of installations of the Flutter alpha version, and several hundred apps built with Flutter have been published.

There is some cost to Flutter’s approach. The Flutter engine is included in each app, adding 6.7 megabytes to each Flutter app on Android, according to the Flutter FAQ. The upside is that the app is faster.

In addition to the “Hamilton” app, which came out in August, Flutter is being used inside Google for critical applications such as its AdWords ad system as well as its Google Shopping Express manager app. Other companies using it include the social media management app Hookle and a chat app for PlanHQ, which sells a cloud-based tool to create business plans.

Although there are many other ways to create mobile apps, even Google doesn’t necessarily view Flutter as a replacement for native application development, or JavaScript for that matter. Mehmet Fidanboylu, a tech lead for an internal mobile app at Google, wrote on Quora in August that progressive web apps likely will remain better for serious apps on powerful enough devices.

Today’s announcement closely follows a reboot of Dart last week to optimize it for client-side development for web and mobile apps. “With Flutter and Dart, developers finally have the opportunity to write production-quality apps for Android, iOS, and the web with no compromises, using a shared codebase,” Dart product manager Anders Thorhauge Sandholm wrote in a blog post. “As a result, team members can fluidly move between platforms and help each other with, e.g., code reviews. So far, we have seen teams like AdWords Express and AppTree share between 50 percent and 70 percent of their code across mobile and web.”

Google didn’t provide a timeframe for a full release but said it will update the beta every four weeks. On the roadmap are the ability to embed Flutter into an existing app, additional support for Google’s Firebase mobile app development platform, an inline web view and inline maps, and a smaller core engine.

Here’s a video on Flutter:

Featured image: Hamilton