Designing a GUI for collaborative applications involves considering the following:

1. User roles and permissions: Define different user roles and permissions to ensure proper access control.

2. Real-time updates: Implement real-time updates to reflect changes made by multiple users.

3. Clear communication: Provide clear communication channels, such as chat or video conferencing.

4. Feedback mechanisms: Incorporate feedback mechanisms, like notifications or alerts, to keep users informed.

5. Collaborative tools: Integrate collaborative tools, such as whiteboards or document editors.

6. User presence indicators: Display user presence indicators to show who is online or active.

7. Conflict resolution: Implement conflict resolution mechanisms to handle simultaneous edits.

8. Version control: Use version control to track changes and maintain a record of revisions.

9. Intuitive interface: Design an intuitive interface that facilitates collaboration.

10. Accessibility: Ensure the GUI is accessible for users with disabilities.

11. Scalability: Design the GUI to scale with the number of users and collaborations.

12. Customization: Allow users to customize their experience and workflow.

Some popular design patterns for collaborative GUIs include:

1. Multiple document interface (MDI)

2. Single document interface (SDI)

3. Tabbed interface

4. Split-screen interface

5. Drag-and-drop functionality

6. Contextual menus and toolbars

7. Real-time commenting and @mentions

By incorporating these elements and design patterns, you can create an effective GUI for collaborative applications that enhances productivity and user experience.