1. 1. Search functionality: The key difference between Read the Docs and Wiki.js is that Read the Docs provides a powerful and efficient search functionality. It allows users to search for specific documentation or content within the documentation by using keywords or phrases. This search functionality makes it easier for users to quickly find the information they need without having to manually browse through the entire documentation.

2. 2. Version control and history: Another important difference is that Read the Docs offers version control and keeps a history of changes made to the documentation. It allows users to track and compare different versions of the documentation, providing a clear audit trail. This feature is crucial for teams working collaboratively on documentation, as it ensures that any modifications or updates can be easily traced and reverted if necessary.

3. 3. User authentication and access control: Read the Docs provides a comprehensive user authentication and access control system. This means that documentation can be restricted to certain users or user groups, ensuring that only authorized individuals can access and modify the content. This feature is particularly useful for organizations that have sensitive or confidential documentation that needs to be protected.

4. 4. Integration with external services: Read the Docs supports seamless integration with external services like GitHub, GitLab, and Bitbucket. This allows users to sync their documentation repositories with these platforms, making it easier to track changes, collaborate with team members, and automate the documentation building and publishing processes. This integration simplifies the workflow for organizations already using these services for version control.

5. 5. Customizability and theming: Wiki.js offers extensive customizability and theming options, allowing users to personalize the appearance and layout of their documentation. It provides a user-friendly interface for customizing the colors, fonts, and overall look of the documentation. This feature is particularly useful for organizations that want to align the documentation with their branding or style guidelines.

6. 6. Real-time collaboration: Wiki.js provides a real-time collaboration feature that allows multiple users to work on the documentation simultaneously. This feature enables teams to collaborate effectively, making it easier to share knowledge, make updates, and communicate in real-time. It enhances productivity and teamwork, especially for distributed or remote teams.

In summary, Read the Docs and Wiki.js differ in terms of their search functionality, version control and history, user authentication and access control, integration with external services, customizability and theming, and real-time collaboration. While Read the Docs excels in providing efficient search, version control, and authentication features, Wiki.js offers extensive customization options and real-time collaboration capabilities.