The key features of a GUI for real-time collaboration include:

1. Real-time updates: Instantly reflect changes made by multiple users.

2. Multi-user editing: Allow multiple users to edit the same document or project simultaneously.

3. Live commenting: Enable users to comment and discuss changes in real-time.

4. @mentions: Allow users to mention and notify each other in comments.

5. Presence indicators: Show which users are online, active, or currently editing.

6. Version control: Track changes and maintain a record of revisions.

7. Conflict resolution: Handle simultaneous edits and resolve conflicts.

8. Live chat or video conferencing: Facilitate real-time communication.

9. Screen sharing: Allow users to share their screens for demonstrations or presentations.

10. Collaborative tools: Integrate tools like whiteboards, mind maps, or document editors.

11. Customizable workflows: Allow users to create custom workflows and processes.

12. Notifications: Provide real-time notifications for changes, comments, and mentions.

13. Mobile accessibility: Ensure the GUI is accessible and functional on mobile devices.

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

15. Security: Implement robust security measures to protect data and user privacy.

By incorporating these features, a GUI can effectively support real-time collaboration, enhance productivity, and facilitate seamless communication among team members.