OpenDSS is a comprehensive electrical system simulation tool for electric utility distribution systems. It technically refers to the open-source implementation of the DSS. It is implemented as both a stand-alone executable program and a COM DLL designed to be driven from a variety of existing software platforms. The executable version adds a basic user interface on to the solution engine to assist users in developing scripts and viewing solutions.

The OpenDSS program has been used for:
1. Distribution Planning and Analysis
2. General Multi-phase AC Circuit Analysis
3. Analysis of Distributed Generation Interconnections
4. Annual Load and Generation Simulations
5. Wind Plant Simulations
6. Analysis of Unusual Transformer Configurations
7. Harmonics and Interharmonics analysis
8. Neutral-to-earth Voltage Simulations
9. Development of IEEE Test feeder cases
10. And more .

The program has several built-in solution modes, including:
1. Snapshot Power Flow
2. Daily Power Flow
3. Yearly Power Flow
4. Harmonics
5. Dynamics
6. Faultstudy
7. And others

Through the COM interface, the user is able to add other solution modes and features externally and perform the functions of the simulator, including definition of the model data. Thus, the DSS could be implemented entirely independently of any database or fixed text file circuit definition.

The license of this software is Free, you can free download and free use this graphing software.