DrawDB
Free, simple, and intuitive online database diagram editor
...You create tables, columns, indexes, and foreign keys via drag-and-drop, and the app keeps relationships clear with clean, orthogonal connectors. It exports DDL for popular SQL dialects so you can move quickly from design to migration scripts. Projects can be saved, shared, and exported as images for documentation, making it useful for handoffs and reviews. The editor supports conveniences like snapping, alignment guides, column type presets, and notes to capture design intent. By centering schema modeling in a fast, approachable UI, drawDB reduces the back-and-forth between whiteboards, spreadsheets, and handwritten SQL.