RDKit

RDKit is an open-source library developed to support cheminformatics and molecular modeling. Implemented in C++, it offers multiple language bindings—including Python—and provides a wide range of functionalities, such as reading and writing molecular structures in SMILES and SDF formats, substructure searching, molecular fingerprinting, and descriptor calculations, as well as 3D structure generation. Because it is freely available under the BSD license, it is actively utilized across various fields, from academic research to industrial applications, including drug discovery, materials science, and integration with machine learning.