Great for hobbyists as well – AudioTools - dB, Sound & Audio Review

I like to build speakers DIY and I use this along with an extension cable and TRRS measurement mic attached to a thin pole to take measurements of my systems. Pink noise through the speaker, and the FFT module with a long decay time, or average mode, allows decent accuracy magnitude response measurements. FFT won't get you the phase response, but the Smaart tools module probably will.
Review by amddude on AudioTools - dB, Sound & Audio.