Aspen Plus is described as 'market-leading process modeling environment for conceptual design, optimization, and performance monitoring for the chemical, polymer, specialty chemical, metals and minerals, and coal power industries'. There are more than 10 alternatives to Aspen Plus for Windows, Linux and Mac. The best alternative is DWSIM, which is both free and Open Source. Other great apps like Aspen Plus are Engineering Equation Solver (Paid), COCO Simulator (Free), Engineering Base by AUCOTEC (Paid) and GateCycle Software (Paid).
GateCycle plant performance monitoring software predicts design and off-design performance of combined cycle plants, fossil boiler plants, nuclear power plants, cogeneration systems, combined heat-and-power plants, advanced gas turbine cycles and many other energy systems.
TRNSYS is a transient systems simulation program with a modular structure. It recognizes a system description language in which the user specifies the components that constitute the system and the manner in which they are connected.
PRO/II® process simulation software is a steady-state simulator enabling improved process design and operational analysis. It is designed to perform rigorous heat and material balance calculations for a wide range of chemical processes.