Callstack Acquires Margelo for Over €20 Million

Polish software firm Callstack has significantly bolstered its engineering capabilities with the acquisition of Vienna-based Margelo. The deal, valued at over €20 million, unites two prominent players in the React Native ecosystem, a cross-platform framework enabling app development for iOS and Android from a single codebase. This strategic move is expected to enhance Callstack's service offerings, particularly for enterprise clients navigating the complexities of mobile application development.

Margelo, founded by Marc Rousavy, has carved out a strong reputation through its impactful open-source contributions. Its Nitro Modules library boasts 34 million downloads, while the VisionCamera framework has seen 40 million downloads, and the react-native-mmkv database has garnered 67 million downloads. Collectively, Margelo's projects have accumulated over 420 million npm downloads, underscoring its deep integration and influence within the React Native community. Beyond its open-source prowess, Margelo also provides custom development and performance optimization services, counting industry giants like Discord, Coinbase, and Expensify among its clientele.

The acquisition aligns with a broader industry shift, as highlighted by both companies. The increasing sophistication of AI tools in accelerating code implementation is pushing the value proposition towards higher-level architectural design, performance tuning, and robust integration. Callstack CEO Mike Grabowski emphasized this point, stating that the integration of Margelo's performance-centric technologies with Callstack's extensive experience in large-scale enterprise deployments will create a formidable force in addressing critical software success factors.

Callstack, established in 2016 shortly after React Native's debut, has grown to employ over 200 professionals and serves more than 100 enterprise customers. The company's focus on guiding organizations through the adoption, scaling, and operation of React Native solutions has made it a key partner for many businesses. This acquisition follows a substantial growth investment received by Callstack in the summer of 2025 from US fund Viking Global Investors, which reportedly valued the company at approximately half a billion Polish Zloty (around €120 million), positioning the Margelo acquisition as a logical next step in its expansion strategy.

Marc Rousavy will continue with the combined entity, leading the development of Margelo's libraries and contributing to the integrated service offerings. His continued involvement, along with his significant stake in the new structure, signals a commitment to sustained innovation. The preservation of Margelo's open-source projects as open source was a key consideration, ensuring continued community access and collaboration. This move is particularly relevant as the React Native market continues its expansion, driven by the demand for efficient cross-platform development solutions.

The integration is poised to expand Callstack's technological portfolio and international reach. By merging Margelo's specialized expertise with Callstack's established enterprise client base, the combined entity aims to offer unparalleled solutions for complex mobile application development challenges. This strategic consolidation reflects the evolving demands of the software development sector, where deep technical expertise and architectural foresight are becoming paramount.