Sofa-an open source framework for medical simulation. SOFA is an open-source, modular mechanical simulation library developed in C++. It includes geometries such as polygonal and volumetric meshes, internal forces such as FEM or springs, ODE solvers such as Explicit or implicit Euler, collision detection methods, OpenGL viewing, and many other features. GPU implementations are available for some force fields, such as springs and tetrahedral FEM. The automatic deployment on multi-core architectures is possible. Its design allows contributors to focus on their domain of competence while reusing other work.