It is an open source EDA tool used for circuit simulation, interactive analysis and PCB design.
You can build the circuit and do the PCB design using eeschema (kicad).
You can also do the simulation of the circuit using Ngpice.
You can build own subcircuit and can also use it for device modeling.
You can think of this tool as an alternative to OrCAD.
For more details, you can visit the eSim website. Please find the link here: http://esim.fossee.in/
FOSSEE aims to promote the open source software and hardware tools for education anddevelopmentpurpose.
Based on the purpose and the field of Application, you can choose the tools.
You can visit the link here for more details: http://fossee.in/