Thermodynamic and kinetic calculations are commonly used for forecasting phase transformations in multicomponent alloys as a function of composition, temperature, and time. They also turn to be very useful for new alloy design. Thus, in the framework of the qualification of existing industrial alloys and the development of new ones (chromium [Cr]-coated zirconium [Zr] alloys, for instance), a new generation of thermodynamic databases has been developed thanks to the systematic use of ab initio calculations. Indeed, density functional theory calculations are significant for the determination of formation enthalpies of stable and metastable phases. Moreover, the special quasirandom structure method is used for the prediction of face-centered cubic, body-centered cubic, and hexagonal closest packed mixing enthalpies in binary solid solutions. The resulting thermodynamic database is a very powerful tool for correctly predicting second-phase precipitate occurrence in industrial alloys and precisely calculate their volume fraction, chemical composition, and existence domain as a function of temperature. The second part of the paper deals with the development of the Ekinox-Zr numerical tool that has been linked to the Zr thermodynamic database using the OpenCalphad Application Software Interface (OCASI) interface of the OpenCalphad software (a free software for multicomponent equilibrium calculations). This tool has been developed to accurately simulate oxide growth and oxygen diffusion into the alloy during high-temperature isothermal oxidation of Zr alloys. The recent developments have been dedicated to the simulation of high-temperature transients showing a good agreement with experimental data.