Schemity

Schemity is a native desktop ERD tool built for software engineers who need a fast, reliable way to design and document database schemas without the friction of cloud-based tools.
Most ERD tools are either too primitive for real-world schema work or bloated with features you never use. Schemity sits in the middle: powerful enough for complex schemas, lightweight enough to install in seconds at just 9MB.
It connects directly to PostgreSQL, MySQL, and SQL Server, reverse-engineering your existing database into a visual diagram instantly. From there, you have full control over the canvas. Relationship lines are freely routable, tables are freely positionable, and nothing is locked behind an auto-layout algorithm you cannot override.
Key features include offline-first architecture, plain JSON schema storage, no account or internet connection required, N:N relationship support with automatic intermediate table generation, and one-time pricing with no subscription.
Schemity is designed around how engineers actually think. You can organize your diagram to reflect domain boundaries, focus on specific areas of a large schema, and use keyboard-driven interactions to move fast. The schema file is plain JSON, so it lives in your repository alongside your code.
It runs on Windows, macOS, and Linux, installs in under a minute, and does not require a cloud account or ongoing subscription. You pay once and own it.
If you have spent time fighting with tools that are too limited, too slow, or require you to be online just to open a diagram, Schemity was built for you.