SoftDFT is a new, open-source software framework for three-dimensional classical density functional theory (cDFT) calculations designed to specifically meet the challenges of modeling complex soft matter systems including charge-regulating polymers and surfaces. Unlike existing cDFT implementations that are limited in dimensionality, flexibility, or scalability, SoftDFT combines advanced free-energy formulations with high-performance numerical sovlers and GPU acceleration within a modular, Julia-based architecture. The framework supports customizable molecular models, interfacial geometries, and boundary conditions enabling accurate and efficient predictions of thermodynamic and structural properties across a broad class of soft matter systems. SoftDFT incorporates state-of-the-art functionals accounting for excluded volume, electrostatic correlations, solvent-mediated interactions, and chain connectivity. As a representative application, we demonstrate SoftDFT's capability through full 3D calculations of weak polyelectrolyte brushes achieving excellent agreement with molecular simulations while reducing computational cost by several orders of magnitude. By integrating with recent advances such as Ising DFT (iDFT) and scalable numerical schemes, SoftDFT provides a transformative platform for predictive modeling of complex fluids. It lowers the barrier to entry for non-experts while offering deep extensibility for developers making it a powerful and accessible tool for the soft matter community.
