DWSIM is an open-source chemical process simulator written in VB.NET, with advanced thermodynamic calculations, reactions support, petroleum characterization / hypothetical component generation tools and a fully-featured graphical user interface. Features: Process Flowsheet Diagram (PFD) drawing Interface VLE calculations using Equations of State, Activity Coefficient and Chao-Seader models Characterization of Petroleum Fractions using bulk properties and/or ASTM/TBP distillation curves and creation of Hypothetical Components using UNIFAC groups Rigorous Distillation/Absorption Column models Support for Chemical Reactions and Reactors Supports ChemSep's Component Database Multivariate Optimization and Sensitivity Analysis utility