low-carbon
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Apollo Atomics
Apollo Atomics is a Cambridge, Massachusetts nuclear startup building the most power-dense pressurized water reactor. By redesigning the steam generator - the bulkiest part of a conventional plant - into a proprietary Compact Steam Generator, the company shrinks a proven reactor design by roughly an order of magnitude, turning a decade-long construction project into a factory-built machine that fits on a truck and deploys in under 24 months. Founded by MIT nuclear PhD Assil Halimi and operator Drew Walker, Apollo is in Y Combinator's Spring 2026 batch and is testing its design in collaboration with MIT.
Tangible
Tangible is a San Francisco climate-tech company that turns static construction drawings and 3D models into live materials data. Its AI-powered platform reads Revit models and PDF drawings to give preconstruction teams structured quantities, cost, and EPD-backed embodied carbon in one place - so developers, contractors, and architects can see the carbon and cost impact of a design and cut both before a building is ever poured. Founded in 2021 by Anneli Tostar and Nicole Granath, Tangible has raised roughly $8.8M and counts builders like Skanska, Prologis, and Hensel Phelps among its users.