1. Project Goals: FeathersJS is designed to be a minimalistic and flexible framework that enables developers to efficiently build scalable applications using JavaScript or TypeScript. On the other hand, NestJS focuses on providing a structured and opinionated approach to building server-side applications using TypeScript and follows the architectural patterns of Angular. While FeathersJS emphasizes flexibility, NestJS emphasizes structure and consistency in code development.

2. Architecture: FeathersJS follows a lightweight, service-oriented architecture where each service represents a resource or a logical component of the application. It allows developers to easily create services and interact with databases using a built-in Object-Document Mapping (ODM) or Object-Relational Mapping (ORM) system. In contrast, NestJS follows a layered architectural pattern with the use of modules, controllers, and providers, following a more traditional MVC (Model-View-Controller) structure. NestJS also leverages decorators for defining routes and dependency injection for efficient modular development.

3. Development Community: FeathersJS has a smaller but highly active development community. It is known for its simplicity and ease of integration with various libraries and databases, making it suitable for quick prototyping and small to medium-sized applications. On the other hand, NestJS has a larger community which benefits from its similarity and alignment with the Angular ecosystem. NestJS is often considered more suitable for enterprise-level applications where robustness and maintainability are crucial.

4. Code Style: FeathersJS encourages developers to have a more flexible and personal coding style, allowing them to choose between different patterns and approaches. This enables developers to build applications rapidly while having control over the codebase. NestJS, being built on TypeScript and following Angular's principles, enforces a more opinionated coding style and structure, making it easier for large teams to collaborate and develop maintainable code. The strictness of the code style can help improve code readability and consistency across large projects.

5. Modularity and Reusability: FeathersJS has a focus on creating modular applications by using services as isolated components. Developers can easily reuse these services in different parts of the application or even in other FeathersJS projects. NestJS, with its support for modules and dependency injection, enables developers to design highly modular and reusable applications. It encourages the separation of concerns and allows for easier code organization and sharing across projects or teams.

6. Testing and Debugging: FeathersJS provides a built-in testing framework and offers easy-to-use debugging tools. It allows developers to write unit tests for services and integrates well with popular testing libraries and tools. NestJS, being based on Angular, inherits its testing capabilities and integrates with the Angular testing ecosystem. It provides a comprehensive testing framework, including unit testing, end-to-end testing, and integration testing. The testing capabilities in NestJS are well-documented and widely used, making it easier for developers to write reliable and robust tests.

In Summary, FeathersJS focuses on flexibility and quick application prototyping while NestJS provides a more opinionated and structured approach, suitable for enterprise-level applications, with an emphasis on modularity and testing capabilities.