The App-a-thon is an intensive 36-hour development marathon where students conceptualise and build functional mobile applications aligned with the UN Sustainable Development Goals. Hosted by the Department of Computer Science, CHRIST (Deemed to be University), Pune Lavasa Campus, and conducted under the BCA301-3: Mobile Applications course, the App-a-thon challenges participants to integrate creativity, technical skill, and teamwork in a dynamic development environment. Supported by Google for Education and Android, the event is guided by resource persons Dr Gobi R, Dr Naived Eapen, Samuel Alex Koshy, and Shriganesh Purohit. During the sprint, learners engage in rapid prototyping, feature implementation, design optimisation, and collaborative planning. Held on 17–18 November 2025 at the Computer Lab, Central Block, the App-a-thon encourages students to solve meaningful real-world problems through technology. It serves as the culminating experience of the Build-it! series, allowing participants to apply their learning and develop impactful solutions, primarily based on the Sustainable Development Goals.