Vienna’s Margelo Joins Poland’s Callstack in a Deal Valuing It Above 20 Million Euros
Trending Topics Jakob Steinschaden
Callstack is buying Vienna’s Margelo, valuing it above 20 million euros. The React Native shop’s open-source tools stay open, and its founder stays on.
Based on reporting by Trending Topics, Jakob Steinschaden — read the original for the full story.
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Polish software company Callstack has agreed to buy Margelo, the Vienna engineering firm best known for open-source work around React Native. The companies announced the deal just now, and the only price tag they’ve made public is a valuation of more than 20 million euros. That keeps the headline simple enough: this is a bet on mobile infrastructure, not a flashy app launch.
Margelo built its name in the React Native world with libraries that developers actually use. Nitro Modules has 34 million downloads, VisionCamera has 40 million, and react-native-mmkv has 67 million. The company says its open-source work has racked up more than 420 million npm downloads in total and more than 800 contributions to the React Native core. Alongside that, it does contract development and performance tuning for app makers.
The client list is the sort that tells you where the work sits: Discord, Coinbase, Expensify, MetaMask, Rainbow, VSCO and WalletConnect all appear on Margelo’s site. The firm says it has around 39 senior engineers, and it was founded and is led by Marc Rousavy, who also maintains the libraries that made it visible in the first place. He says the company started as a leap into the unknown five years ago, after he dropped out of an economics degree three days in.
Callstack is older and much larger. It was founded in 2016 in Wrocław, a few months after Meta released React Native, and it says it now has more than 200 people serving over 100 enterprise clients. It is also a founding member of the React Foundation, the body Meta created to steward React and React Native. Last summer, Viking Global Investors backed Callstack with a growth investment that the company said valued it at roughly half a billion zloty, about 120 million euros.
The companies have not disclosed the purchase price or how the deal is structured, and there’s no closing date or regulatory timetable yet. But the intent is clear enough. Callstack wants Margelo’s technology for its enterprise customers, and both sides are framing the deal around AI pushing engineering value toward architecture, performance, native integration, validation and safe releases. Rousavy stays on to keep building the libraries, and the open-source projects will remain open source.
My take — AI-written commentary, not fact-checked reporting
This is the kind of deal that makes sense precisely because it’s boring in the right places. The open-source maintainer gets a bigger platform, the enterprise shop gets credibility with developers, and everyone gets to say “AI” without pretending code itself is the whole business. Open source still looks strongest when the acquirer doesn’t try to lock the door behind it.
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