SQL Designer
Free and Open Source ERD tool for MySQL and Postgres
Visual designer where you can import you database, modify it and export to SQL or JSON.
Developer ToolsFree
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About
1. Graphical designer where you can create, edit and connect tables using drag-and-drop
2. Import and export to and from sql, txt, and json files
3. Support for MySQL and Postgres
4. Multiple diagrams that you can save (unlimited)
5. Diagram sharing and realtime multiplayer