Abstract One of the most topical problems of drilling mechanics is development of a software program for 3D string dynamic simulation in a 3D well on various operation regimes with maximum account of all external factors. The paper describes the results of long-term development of general-purpose DYNTUB software designed for string dynamic simulation. The software calculates: String torque and drag;Drillstring lateral and torsional vibrations;Drillstring buckling and whirling;Well path while drilling in sliding regime and in rotary regime with Rotary Steerable Systems (RSS) or systems controlled by downhole motor angular velocity modulation;Standoffs between the casing and the wellbore wall with various centralizers. The software is based on the stiff string dynamic model. It accounts for deformation of the wellbore walls contacted by the string, initial drill pipe bending, PDC bit interaction with the bottomhole under downhole and pore pressure, rock anisotropy, refined multicomponent string friction model, etc. The software proved applicability of the "soft" drill string model to calculate torque and drag, enabled study of multicomponent friction effects on string buckling, well path calculation while RSS drilling, and solving other complex problems of drilling mechanics. Software efficiency is demonstrated based on case studies; the paper also includes results of comparative analysis using data from other references. The software is designed for expert analysis of drilling, casing, coil tubing and similar object parameters while well drilling and completion.