Who uses supercomputers?

Answer 1

Supercomputers are computers designed to have roughly an order of magnitude or more higher performance than the then current state of the art standard computers. They are used for solving particularly computationally difficult problems that could not be done by other methods in a reasonable time so as to be useful. Some typical uses:

• Airflow models for aircraft, spacecraft, vehicles, wind turbine blades, etc. when using models in windtunnels would be impractical
• Nuclear weapons design and analysis
• Nuclear reactor design and analysis
• Petroleum oil field analysis based on collected acoustic data
• Cryptanalysis
• Long term weather forecasting
• Modeling of the electric transmission grid
• Aquifer models
• Combustion models for jet engines, car engines, rocket engines, etc.
• Firing tables for artillery pieces
• etc.

Of course what is one day's supercomputer is obsolete the next day as performance of standard computers advances. Same as with any other computer.

Answer 2

It is mainly used by scientists, military, and meteorologists