Arduino can be used readily as an oscilloscope using a simple arduino program and a simple interface using a Processing program. See example at https://www.hackster.io/lucian_vdo/arduino-oscilloscope-9eb08b
- Good for 5 kHz
- Requires a computer with display, so not that practical when it comes to mobility
- Would want a standalone Arduino oscilloscope.
- A poor man's oscilloscope is an Arduino connected via USB to a computer which uses a Processing code running on your computer - https://www.build-electronic-circuits.com/arduino-oscilloscope/
- Using a Complex Programmable Logic Device (like FPGA but simpler) Arduino shield - 
- From scratch by a physics guy - not complete - 
- Using Processing with good visual interface, 4 channel -