1. Integration with Tools: Shippable offers integrations with third-party tools like JIRA, Slack, and Docker Hub, while Zuul CI focuses on integrating with GitHub, Gerrit, and Jenkins for a more streamlined development process.

2. Scalability: Shippable provides scalability through container-based builds and parallel testing, whereas Zuul CI emphasizes distributed pipelines for efficient scaling across large projects and organizations.

3. Configuration Management: Shippable uses a YAML-based configuration for defining CI/CD pipelines, whereas Zuul CI utilizes Ansible playbooks for configuring jobs, allowing for more robust and flexible automation capabilities.

4. Support for Multi-Cloud Environments: Shippable offers support for deploying to various cloud platforms like AWS and Azure, whereas Zuul CI focuses on OpenStack as its primary cloud provider, catering to organizations heavily invested in OpenStack infrastructures.

5. Community and Documentation: Shippable has a larger and more active user community, with extensive documentation and tutorials available, while Zuul CI has a more niche user base with comprehensive technical documentation for advanced users.

6. Customization and Extensibility: Shippable provides a user-friendly interface for customizing workflows and integrating with external tools through plugins, whereas Zuul CI offers extensive customization through its flexible Python-based configuration, allowing for more intricate automation scenarios.

In Summary, Shippable and Zuul CI differ in their tool integrations, scalability approaches, configuration management methods, cloud environment support, community size, and customization/extensibility options.