1. Template Syntax: Nunjucks uses a syntax similar to traditional HTML, with tags and expressions enclosed in double curly braces, while Pug uses a simplified and indentation-based syntax with nested tags represented by indentation levels and no closing tags required.
2. Whitespace Handling: Nunjucks preserves the whitespace in the code, including leading and trailing whitespace, while Pug automatically removes unnecessary whitespace, resulting in cleaner and more compact code.
3. Extensibility: Nunjucks provides a wide range of filters, macros, and global variables that can be easily customized and extended, allowing for more flexibility in the template rendering process, whereas Pug has a limited set of built-in filters and does not support macros, making it less extensible.
4. Error Handling: Nunjucks has a more robust error handling system, providing detailed error messages with line numbers and file names, making it easier to debug and troubleshoot, while Pug's error messages are often less informative and may require additional effort to identify and fix.
5. JS Integration: Nunjucks has seamless integration with JavaScript, allowing you to easily include JavaScript code within your templates and execute functions, whereas Pug has limited support for JavaScript integration, making it less suitable for projects that heavily rely on JavaScript interactions.
6. Community and Support: Nunjucks has a larger and more active community, with extensive documentation, tutorials, and resources available, making it easier to find support and resolve issues, whereas Pug has a smaller community and fewer resources, which may make it more challenging to find help and resources when needed.

In Summary, Nunjucks and Pug have significant differences in their template syntax, whitespace handling, extensibility, error handling, JavaScript integration, and community and support.