Appsemble is an open-source low-code platform that allows public administrations to design and implement Progressive Web Apps (PWAs) through modular components. Its architecture supports reuse, interoperability, and collaboration across the public sector. The platform includes a repository of building blocks and applications aimed at fostering shared development efforts and digital innovation within governmental contexts. All source code is published under an open-source license (AGPL) and is publicly available via https://github.com/appsemble. The solution emphasizes transparency, extensibility, and alignment with digital sovereignty goals in the European public sector.