Gaphor

Gaphor is a modeling application that supports UML, SysML, RAAML and the C4 architectural notation. It provides a fully‑compliant UML 2 data model, allowing users to create both simple visualizations and detailed, complex system models rather than just static pictures. The tool runs on Windows, macOS and Linux and is distributed under the Apache 2 license, with its code written in Python.

The interface is diagram‑centric, showing all model information directly in the visual representation without hidden property panels. Users can build class, interaction, state‑machine, block‑definition, requirements and other diagram types, and can mix elements from different notations on a single canvas. Built‑in styling, dark mode and a tree view help navigate large models.

Gaphor is extensible through plug‑ins that add code generation, export capabilities or custom extensions, accessible via the graphical interface or command line. It targets casual modelers as well as model‑driven development experts, offering a consistent, standards‑compliant environment without vendor lock‑in.