Computational thermodynamics has become an essential tool to overcome the inconveniences of trial-and-error experiments in order to optimize processing routes and design new alloys. In particular, the CalPhaD (Calculation of Phase Diagrams) method uses the Gibbs energy of individual phases parameterized with the multicomponent compound energy formalism to calculate thermodynamics equilibria in complex multicomponent alloys [1] [2]. In this work, we will highlight recent applications of the CalPhaD method to the development of advanced new alloys, such as High Entropy Alloys (HEAs), and the exploration and optimization of processing parameters for additive manufacturing of functionally-graded materials (FGMs). Within the scope of HEA design, we will focus on the development of novel CoNi-based High Entropy HEAs for high-temperature applications and preliminary work on the development of HEAs for hydrogen storage applications. In the scope of FGMs, we will show how CalPhaD-based calculations can support additive manufacturing of compositionally graded material mixing a Ni-based superalloy (Inconel 718) and a stainless steel (316L) produced by direct energy deposition (DED) technology. While the central focus of the presentation is on the use of the CalPhaD method applied to these use cases, all aspects of the study are closely combined with experimental characterization of microstructures and properties, using state-of-the-art techniques, such as electron microscopy (SEM, EDX, EBSD), dilatometry, and micromechanical testing (micro and nanohardness mapping).