Oscar Ender developed core backend features for the PowerMate and FunkoShop-Backend repositories, focusing on robust data modeling and API design using Java, Spring Boot, and JPA/Hibernate. He implemented a consumption tracking API and data model in PowerMate, aligning service and controller layers for maintainability and future extensibility. In FunkoShop-Backend, Oscar scaffolded and tested a comprehensive ProductController, delivering endpoints for CRUD operations, advanced product listings, and recently added product retrieval. He expanded test coverage with JUnit and Mockito, improved documentation with UML diagrams, and streamlined configuration management, resulting in stable, well-documented APIs that support efficient onboarding and iterative development.