Observed Signal · Aug 26, 2026 · M&A - Announced · Source: Trending Topics · Impact: 2/5 · Sentiment: Positive
Callstack Acquires Margelo for €20M; Osmund Energy Exits Stealth
Two key European tech developments have been announced. First, Danish energy startup os.energy exited stealth, launching Osmund, a zero-margin digital electricity app providing power at cost-price. To scale its platform, os.energy secured a €1 million pre-seed investment from Copenhagen's PSV Tech. Second, Polish software firm Callstack acquired Vienna-based React Native specialist Margelo in a deal valuing Margelo at over €20 million. Renowned for open-source mobile libraries like VisionCamera with over 420 million total downloads, Margelo serves major clients including Discord and Coinbase. Callstack leveraged capital from its 2025 growth investment by Viking Global Investors, which previously valued Callstack at approximately €120 million, to fund the acquisition. Post-acquisition, Margelo's founder Marc Rousavy will remain as a shareholder, and its libraries will continue under open licensing.
The acquisition of Margelo by Callstack consolidated two prominent React Native development and mobile architecture players, directly impacting the web and mobile application ecosystem.
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Key Takeaways & Evidence Grounding
- Danish energy startup os.energy emerged from stealth, launching Osmund, a digital power app providing electricity at cost-price with no usage margin.
- os.energy secured a €1 million pre-seed funding round led by Copenhagen-based early-stage venture firm PSV Tech.
- Polish software development company Callstack acquired Vienna-based mobile engineering firm Margelo in a transaction valuing the target at over €20 million.
- Margelo is a prominent React Native developer whose open-source libraries, including VisionCamera, have achieved over 420 million total downloads.
- Callstack utilized capital from its 2025 growth investment by Viking Global Investors, which valued Callstack at approximately €120 million, to fund the acquisition.
Connected Companies & Entities
8 Entities mapped“Polish software company Callstack is acquiring Vienna-based engineering firm Margelo....”
“Polish software company Callstack is acquiring Vienna-based engineering firm Margelo....”
“Margelo lists Discord, Coinbase, Expensify, MetaMask, Rainbow, VSCO and WalletConnect among its references......”
“Margelo lists Discord, Coinbase, Expensify, MetaMask, Rainbow, VSCO and WalletConnect among its references......”
“Margelo lists Discord, Coinbase, Expensify, MetaMask, Rainbow, VSCO and WalletConnect among its references......”
“Margelo lists Discord, Coinbase, Expensify, MetaMask, Rainbow, VSCO and WalletConnect among its references......”
“Its finances got a boost last summer, when US fund Viking Global Investors came in with a growth investment that valued Callstack at roughly...”
“Callstack was founded in 2016 in Wrocław, a few months after Meta released React Native....”
Ontology Mapping & Concepts
Related Market Signals & Shifts
Recent verified developments and strategic activity across this market segment.
Callstack Acquires Vienna-Based Margelo in €20 Million Deal
Polish software firm Callstack has acquired Vienna-based React Native specialist Margelo in a deal valuing the company at over €20 million. Supported by a recent €120 million (500 million PLN) valuation from Viking Global Investors, the merger unites two cross-platform mobile development leaders to address the rise of AI-driven engineering and enterprise app architecture. Margelo is highly regarded for high-performance open-source libraries like VisionCamera and react-native-mmkv, boasting over 420 million downloads for clients including Discord and Coinbase. Margelo founder Marc Rousavy will remain as director of mobile architecture. Separately, US DefenseTech startup Mara raised $7 million in pre-seed funding led by Khosla Ventures to develop Spike, an autonomous kinetic drone defense system. The AI-guided tracking system has already undergone field testing with Ukrainian forces and the US Army in Europe and Texas.
Callstack Acquires Margelo; Sam Altman Custom OpenAI Watches
Polish software development agency Callstack has acquired Vienna-based mobile engineering firm Margelo in a deal valuing Margelo at over 20 million euros. Margelo, founded by Marc Rousavy, is highly regarded in the React Native community for its widely downloaded open-source libraries like Nitro Modules and VisionCamera. Post-acquisition, Rousavy will continue to lead Margelo's open-source projects while becoming a Callstack shareholder. Separately, OpenAI CEO Sam Altman has commissioned seven custom titanium luxury watches from Swiss manufacturer Vanguart for OpenAI's leadership, featuring branding, AI-themed engravings, and Python-inspired messages on the casebacks.
Callstack Acquires Margelo for €20M; Bitcoin Hits $80,000
In August 2026, Polish software company Callstack announced the acquisition of Vienna-based mobile engineering firm Margelo, valuing the company at over €20 million. Both companies specialize in React Native, a prominent cross-platform application framework. Margelo is highly regarded for its open-source libraries, such as Nitro Modules and VisionCamera, which have amassed hundreds of millions of downloads. Concurrently, the global cryptocurrency market experienced a major rally, with Bitcoin stabilizing near $80,000 ahead of the Federal Reserve's Jackson Hole symposium. This year's summit, led by Fed Chair Kevin Warsh, features a program focused on financial innovation and digital payments, directly intersecting with the blockchain and digital assets ecosystem.
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