DWSIM is a multiplatform, CAPE-OPEN compliant chemical process simulator for Windows, Linux, Android, macOS, and iOS. It is available for download from here.

DWSIM allows chemical engineering students and practicing engineers to model process plants using rigorous thermodynamic and unit operations models. Since DWSIM is free/libre and open-source, they can see how the calculations are being done by inspecting the code during execution using free/libre tools available elsewhere.

DWSIM's powerful Thermodynamics engine is also available as a standalone dynamic link library (DLL) that can be linked against proprietary applications.