1. Hosting: Bitbucket Pipelines is a cloud-based CI/CD tool integrated directly into Bitbucket Cloud, while Zuul CI can be self-hosted and run on private infrastructure, offering greater control over the environment.
2. Configuration Language: Bitbucket Pipelines uses a YAML configuration file for defining build pipelines, whereas Zuul CI employs a unique Ansible-based configuration language known as Zuul v3.
3. Scaling: Bitbucket Pipelines is better suited for small to medium-sized projects due to its limited scalability, whereas Zuul CI is designed to handle complex and large-scale CI/CD workflows efficiently.
4. Integration: Bitbucket Pipelines seamlessly integrates with Bitbucket repositories, providing a streamlined experience for development teams using Bitbucket Cloud, whereas Zuul CI can integrate with a variety of version control systems and collaboration tools, offering more flexibility in toolchain selection.
5. Community Support: Bitbucket Pipelines benefits from the large user base and community support of Atlassian products, providing access to a wide range of resources and documentation, whereas Zuul CI, being an open-source project by the OpenStack Foundation, has a strong community backing with contributions from various organizations.
6. Parallelism and Dependency Management: Bitbucket Pipelines lacks advanced features for parallelism and dependency management between jobs, while Zuul CI offers sophisticated options for managing dependencies and orchestrating complex job executions within pipelines.

In Summary, Bitbucket Pipelines is a cloud-based tool closely integrated with Bitbucket Cloud, whereas Zuul CI is a self-hosted CI/CD solution with advanced features and greater scalability options.