GTSAM

Georgia Tech Smoothing and Mapping — a C++ library for factor graph-based optimization, widely used in SLAM, visual-inertial odometry, and sensor fusion. GTSAM provides efficient implementations of incremental solvers (iSAM2), nonlinear optimization (Levenberg-Marquardt), and probabilistic inference on factor graphs. It is the backend of many state-of-the-art SLAM systems.