The open-source Chemistry Development Kit (CDK) platform is a collection of Java libraries for chemoinformatics applications, also including the calculation of molecular descriptors. Examples of graphical user interfaces (GUI) to calculate CDK-based molecular descriptors are the PaDEL software and the CDK Descriptor Calculator GUI by Guha. The BlueDesc calculator is a command-line tool that converts an MDL SDFile into ARFF and LIBSVM formats with up to 174 descriptors using CDK and JOELib2. Tetko coordinated the implementation of thousands of descriptors from different chemoinformatics groups and packages in the OCHEM free web service, which is also a portal for the training of QSPR models. ChemDes is another free web service that integrates several available packages to calculate 3679 molecular descriptors and 59 types of molecular fingerprints. Proprietary software for the processing of molecular structures often include the ability to calculate molecular descriptors; examples are MOE, 8 VolSurf+, CORINA Symphony, 10 ChemAxon Calculator Plugins, and alvaDesc. The Python open-source RDKit software has implemented a wide range of chemoinformatics tools, including the calculation of molecular descriptors, and is currently much used in machine learning projects. The Mordred software is a Python package designed to calculate molecular descriptors, some with RDKit wrappers, others with original implementations; it is provided for command-line use or as a web application.