Composite structures have been extensively used in numerous engineering applications. The Finite Element Method (FEM) is the standard numerical technique to perform structural analysis of composite structures, such as plates and shells made of functionally graded materials or fiber reinforced laminate composites. The Isogeometric Analysis (IGA) is an alternative to FEM that uses robust rational basis functions from CAD systems to approximate solution fields [1]. This work presents FAST (Finite element AnalySis Tool), an open source FEM and IGA framework for structural analysis of composite structures [3, 4]. The code is developed in C++ language using Object-Oriented Programming concepts [2]. The software features FEM and IGA static and dynamic analyses considering material and geometric nonlinearities. The system supports various types of elements for structural analysis of composite structures, as continuous elements (plane stress and 3D solid) and structural elements (plates and shells), for triangular, quadrilateral and hexahedral standard FEM shapes (e.g. T6, Q8, and Brick20) and IGA shapes (e.g. B´ezier triangles, NURBS surfaces and solids). The software architecture was designed to accommodate both FEM and IGA using similar classes, interface routines, and data structures. Moreover, the system incorporated FE2 multiscale analysis, which allows for the simulation of complex material behavior at the microstructure level.The system architecture is detailed using UML diagrams, highlighting the modifications required to incorporate IGA and FE2 modules. The computational implementation is validated using nonlinear examples of laminated and functionally graded plates and shells. FE2 module is employed in the analysis of particulate composites with a metallic matrix and ceramic inclusions. The obtained results are in agreement with the results available in the literature. FAST is available at https://github.com/lmcv-ufc/FAST.