ceo and founder @margelo_com (acq by @callstackio) – angel investor - hobby racing driver - I built VisionCamera, Nitro and react-native-mmkv

Vienna, Austria
Joined September 2014
Pinned Tweet
Big News: Margelo has been acquired by @callstackio for over EUR 20 million. πŸ₯³ I founded Margelo 5 years ago, knowing nothing about business - I actually dropped out of economics university after 3 days. We built our reputation for high-end performance software through open-source libraries like VisionCamera (40M downloads) and react-native-mmkv (67M downloads), and quickly landed high-profile clients like Discord, Coinbase, Expensify and VSCO. Two years ago we doubled down on mobile architecture with Nitro (34M downloads), which gained rapid adoption in the community and allowed us to bring even more ideas to life. I’ve been friends with Mike from Callstack for a long time, which makes me even more excited to remain a significant shareholder and bring mobile technology to a whole new level. I'd like to thank my team for shaping Margelo into what it is today. ❀️
πŸŽ‰ @margelo_com Joins Callstack to Advance High-Performance React Native Engineering Vienna, Austria. 1 September 2026.Β Callstack, a leader in React Native and cross-platform development, today announced that Margelo, the Vienna-based high-end engineering company behind Nitro Modules, VisionCamera and 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.
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Friendly reminder that our Codex Mobile Dev plugin also supports native iOS and Android development πŸ’Œ
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Nitro V1 is almost done, I just merged Android support (48 PRs! 🀯)
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New storage tool coming in the next release of the Codex Mobile Dev plugin βœ¨πŸ“¦
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I just decoupled Nitro from react-native. The new package "πš—πš’πšπš›πš˜-πšŒπš˜πš›πšŽ" exposes all portable native APIs, JS bindings and TypeScript types. This makes it easier for other frameworks (like @LynxJS_org or @NativeScript) to adopt Nitro - all they need is JSI. Almost all JS Runtimes have JSI implementations: Hermes, V8, JSC, SpiderMonkey, Chakra, etc. We also now test πš—πš’πšπš›πš˜-πšŒπš˜πš›πšŽ standalone on Hermes, without react-native. πš›πšŽπšŠπšŒπš-πš—πšŠπšπš’πšŸπšŽ-πš—πš’πšπš›πš˜-πš–πš˜πšπšžπš•πšŽπšœ remains inside the repo and stays one of the official targets. It contains react-native specific setup (like autolinking and .podspec), and react-native specific features like π™·πš’πš‹πš›πš’πšπš…πš’πšŽπš  that was previously inside nitro. As part of this, πš—πš’πšπš›πš˜πšπšŽπš— will receive a plugin system soon so we can fully lift out π™·πš’πš‹πš›πš’πšπš…πš’πšŽπš  and other RN specific features. This could set the foundation for third party language targets (like Rust) too. Nitro V1 is 70% done and will be a breaking change for library authors.
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Maybe we could get nitro into react-native core now that it's decoupled? πŸ‘€ @cortinico
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this is the most impressive shit i've ever seen
Real life, baby
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I made πšœπš πš’πšπš::πš‚πšπš›πš’πš—πš up to 60% faster
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The idea is to avoid expensive value witness operations in favor of simple πšœπš πš’πšπš_πš›πšŽπšπšŠπš’πš— and πšœπš πš’πšπš_πš›πšŽπš•πšŽπšŠπšœπšŽ calls. github.com/swiftlang/swift/p…
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I recreated Minecraft with Claude, entirely in C. 60+ FPS on a 1.2 GHz dual-core CPU. No dedicated GPU.
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Marc retweeted
Today we're standing up XBOX LABS (labs.xbox.com). Here is the note that I sent to the team: Team, The first video games emerged some 75 years ago. In the time since, there have been booms and busts, but every year there are more great games to play, more devices to play them, and best of all, more people than ever playing. That growth helped make XBOX what it is today, and we've helped shape the industry in return, from bringing hard drives to consoles and online gaming through Xbox Live to Game Pass and cloud gaming, alongside franchises that have brought millions of people together. In recent weeks, we've seen games rapidly decompiled and rebuilt to run on hardware they were never originally designed to support. Windows PC builds have been translated to run on Apple Silicon or ported to run inside a browser through WebAssembly and WebGPU, the latter now approaching 90% global browser support. Perhaps more surprisingly, we've seen many of the biggest games in the world have been remixed into the source code of another. These experiments challenge long-held assumptions about our industry: the tether between software and hardware, the boundary between creation and play, and how people discover and experience games. While it is hard to predict the future of gaming, it is easy to see the possibilities in making great games easier to access, giving old games new life and allowing more players to become creators and co-creators. These are unmistakably good outcomes for players, even when (and sometimes because) they challenge our existing business models. To explore these possibilities, I’ve asked Scott to stand-up XBOX LABS, a small group of game makers, engineers and scientists whose job is to turn emerging ideas into things our players and developers can experience. We'll build in the open, learn from what people do, and measure success by whether more people are playing and creating. I think XBOX has an important role to play here. Coding became the first major workload for agents because they can write, run, and test software. Games share many of those same properties, and people spend more than 72 billion hours a year playing XBOX games, roughly five times the estimated time spent writing code worldwide. We've spent 25 years learning how to make great games, and I want our game makers to help shape what these new technologies make possible. As we learn, we’ll share the tools we build with developers across the industry, just as we always have. Our priorities aren't changing. We remain committed to the 4Cs, to making great games, to our hardware and to being responsible stewards of IP and the communities built around it. LABS gives us a way to explore new technology that is game design led without abandoning the work already underway. Asha
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We trained Apex for React Native. It landed #2 at fixing web React. Callstack's Apex is tied #5 overall on @aidenybai's ReactBench. React Native tuning carries over to the web. Try it on Vercel AI Gateway or apex.callstack.com
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Nitro's new HybridClass concept is actually faster than a pure JS class in react-native (because of the Babel transform).
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Nitro on NativeScipt!!! 😍😍😍
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Another Swift Compiler PR merged
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No way, the author of πš›πšŽπšŠπšŒπš-πš—πšŠπšπš’πšŸπšŽ-𝚏𝚊𝚜𝚝-πš’πš–πšŠπšπšŽ is back 🀯
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Marc retweeted
Introducing One 2. React Native’s problem? It takes 100 packages to feel native. Now it takes just One. Think Bun for cross-platform: All-in-one, fast in every way, only three letters. npx one
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insane performance numbers
react-native-better-pdf 1.0 is out πŸ“„ A native PDF viewer for React Native, built on @mrousavy's Nitro Views. Opens a 1,000-page PDF in 91 ms. react-native-pdf: 746 ms. PDFKit on iOS, PdfRenderer on Android. No PDFium, no WebView, no JS in the scroll path.
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Don't get me wrong I'm all for new ideas - but who tf chooses Dart over JavaScript or Swift???
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