The applications of a Butterworth filter are listed below:

• Because of the maximal flat frequency response in the passband, it is used as an anti-aliasing filter in data converter applications.

• The Butterworth filter is used in the audio processing application. An efficient audio noise reduction tool can be developed using a Butterworth filter.

• It is also used in various communication and control systems.

• It is used in radar to design the display of radar target tracking.

• It is used for motion analysis.

Reference:

https://www.electrical4u.com/butterworth-filter/