What are the most popular open-source projects? Given the size and scope of the tech industry, that might seem like an impossible question to answer—but GitHub, with its annual State of the Octoverse report, actually gives us a pretty good idea.

For the uninitiated, GitHub is a massive code repository (along with some tools for things like bug tracking and feature requests). It’s used by tens of millions of people, so whatever behavior you see on it is a pretty good barometer of some tech-industry trends.

When it comes to open-source projects, the top ones draw tens of thousands of contributors. However, there’s also a fair amount of churn in the upper rankings, suggesting that even the most popular projects face risk of abandonment if they don’t deliver what developers and users ultimately need. “Two have been on this list since 2016 : microsoft/vscode and ansible/ansible,” explained the Octoverse report. “New in 2019 are flutter/flutterfirstcontributions/first-contributions, and home-assistant/home-assistant.”

Here’s the full breakdown of the top 10 most popular open source projects:

When projects become popular, they also enjoy considerable spikes in contributions, as the following list demonstrates. “Kits and frameworks for building apps and websites across languages and platforms are seeing contributor growth this year,” the report added. “Since its 1.0 release in December 2018, flutter/flutter has climbed to #2.”

What’s the bottom line here? If you build apps, study Flutter, which is a cross-platform framework. At its I/O 2019 conference, Google announced that Flutter was now available as a cross-platform user interface design platform, applicable to both website and desktop apps, IoT, and so on. It’s clear that developers are really interested in the platform, at least based on the contributor levels. (It’s a similar story with React Native, another app-building framework for iOS, Android, and the web; but while React Native was a top open-source project, it’s not among the fastest-growing.)

The presence of TensorFlow among the top open-source projects suggests that more and more developers are interested in exploring artificial intelligence (A.I.) and machine learning. TensorFlow is a popular machine-learning library (and one of the highest-paying tech skills of 2018, just by the way) released by Google under an Apache 2.0 open-source license. Developers can use TensorFlow libraries in their codebases to speed up machine-learning processes.

If you’re just exploring the open-source world for the first time, check out the Octoverse report for a full breakdown of what people interested in—and feel free to contribute, of course, if you have something valuable to add.