Netgen is a tool for comparing netlists, a process known as LVS,
which stands for "Layout vs. Schematic". This is an important step
in the integrated circuit design flow, ensuring that the geometry
that has been laid out matches the expected circuit.
The greatest need for LVS is in large analog or mixed-signal circuits
that cannot be simulated in reasonable time. Even for small circuits,
LVS can be done much faster than simulation, and provides feedback
that makes it easier to find an error than does a simulation.