🎉 @margelo_com Joins Callstack to Advance High-Performance React Native Engineering

Vienna, Austria. 1 September 2026. Callstack, a leader in React Native and cross-platform development, today announced that Margelo, the Vienna-based high-end engineering company behind Nitro nd react-native-mmkv, is joining Callstack in a transaction valuing Margelo at more than EUR 20 million.

Margelo builds high-performance technology for React Native. Nitro Modules (34M downloads) lets developers write fast, type-safe native modules in C++, Swift or Kotlin, and quickly gained widespread traction across the ecosystem. VisionCamera (40M downloads), Margelo's enterprise-grade open-source Camera framework and react-native-mmkv (67M downloads), a key-value storage library, power countless React Native apps today.

Callstack has spent a decade helping large organizations adopt, scale and operate React Native, contributing to the framework and its open-source ecosystem along the way.

Together, the two teams give clients the strongest React Native performance expertise in the market, backed by delivery proven in complex enterprise environments. Margelo's technology and Callstack's delivery experience will now be available to the same clients.

The timing reflects a fundamental change in how software is built. AI is making implementation faster and cheaper, but architecture, performance, native integration, validation and release safety are becoming more important, not less. These are the fundamentals on which both companies have built their reputations and on which they will continue to build together.

"Margelo has built some of the strongest performance technology in React Native. Callstack has spent a decade helping large organizations adopt and scale the framework. Bringing those strengths together gives us the team and reach to solve more of the hard problems that determine whether software succeeds in production," said Mike Grabowski, CEO and Founder of Callstack.

"At Margelo, we’ve built high-performance technology that developers already rely on. We’re excited to partner with Callstack to bring it to more clients and scale its impact. As software development becomes increasingly agentic, we want that technology to provide the foundation teams need to build reliable software with agents," said Marc Rousavy, CEO and Founder of Margelo.

Margelo's existing open-source libraries will remain open source. Marc will continue to lead their development and help shape the combined company's offering.

The transaction follows Callstack's 2025 growth investment and supports its strategy to expand technology and open-source capabilities while growing internationally.

guess who's back

When the way software is built changes, we help companies adopt it.

For over a decade, that meant bringing React Native to production across mobile, web, desktop, and TV.

Now we are expanding that same mission to AI-native engineering: helping teams ship software with agents, his is our new manifesto.

Introducing Brownie 🍫

An end-to-end type-safe store for your React Native Brownfield apps🔒

It's a storage solution that bridges the gap between two worlds. It will make your brownfield integrations much easier.

Check out this quick walkthrough ⬇️

Long time coming! @swmansion was quietly building this for last 3+ years. Amazing work, congrats 🎉

And you can try it today with Rock:

𝚛𝚘𝚌𝚔 𝚛𝚞𝚗:𝚑𝚊𝚛𝚖𝚘𝚗𝚢

Here’s a little showcase

We just landed an experimental support for HarmonyOS Next platform 🚀

𝚛𝚘𝚌𝚔 𝚛𝚞𝚗:𝚑𝚊𝚛𝚖𝚘𝚗𝚢

Next on the list: Vega OS

We're building on that Open Source foundation, and updating it with your favorite features, such as local and remote caching (the GitHub Action is not ready yet).

The HarmonyOS Next platform is quite new, and there's still a lot to build there. We're happy to provide developers with better tools to help them iterate quickly, and we can't wait to see what you'll build.

Happy experimenting! 💥

Amazon just dropped their own OS that has React Native BAKED IN 🤯.

We're excited to announce React Conf speakers from some of your favorite React frameworks and build tools like @expo, @nextjs, @parceljs, @ReactRouter, @RedwoodJS, @rockjs_dev, and TanStack

Thank you for over 500 stars ✨

And don’t forget star 🌟 the project if you liked it github.com/callstack/rock

Step-by-step, code-first, and written by the devs who built the tooling.

Our new ebook is your guide to integrating React Native into native apps in a modular, gradual, and production-ready way

Includes:
✅ Packaging configs
✅ XCFrameworks & AARs
✅ Brownfield best practices

Enjoy faster @rockjs_dev v0.11:
- bundled create-rock for instant startup
- improved fingerprints
- iOS prebuilds by default

Good things start with a single piece of rock

In next release: `npm create rock` will get up to 5x faster

chatted with @Huxpro for few hours today about @LynxJS_org

very bullish, amazing stuff coming soon 👀