DUST is an open-source mid-fidelity aerodynamic code initially deeloped from a collaboration between Politecnico di Milano and A^3 by Airbus LLC (www.dust-project.org ↗). DUST provides several models for both aircraft components and wake evolution to obtain fast and reliable aerodynamic simulations of VTOL aircraft of arbitrary configurations. DUST is an open source code developed under MIT license. The code exploits the Object Oriented paradigms of the latest Fortran standards to obtain a coherent formulation of the aerodynamic problem, simultaneously involving different modelling techniques. The mathematical formulation of the problem relies on the Helmholtz's decomposition of the velocity field to recast the aerodynamic problem as a combination of a boundary value problem for the potential part of the velocity and a mixed panels-vortex particles model of the free vorticity in the flow. The mixed panel wake-vortex particle model provides a stable Lagrangian description of the free vorticity field in the flow, suitable for numerical simulations with strong aerodynamic interactions. DUST was deeply used for the aerodynamic characterization of interactional aerodynamics typical of eVTOL aircraft and tiltrotors and was coupled with the multibody software MBDyn to perform aeroelastic simulation of complex rotorcraft vehicles.