How would you approach merging two similar applications, one 10 years old and the other 3 years old? Would you create a new application or enhance one of the existing apps?

My approach would begin with a thorough assessment of both applications. This includes a deep dive into their architectures, evaluating the technology stack, scalability, performance, and maintainability of each. I'd also scrutinize the codebase quality, structure, and documentation. This foundational understanding will dictate whether to refactor the older application, migrate functionality to the newer one, or build a new application from scratch, prioritizing a solution that offers long-term stability and adaptability.