The Voxengo SPAN has a free version, Very useful for seeing mastering levels. It is recommended to be at -30db for the low-ends after mastering.
https://www.voxengo.com/product/span/
https://www.meldaproduction.com/MFreeFXBundle
https://hofa-plugins.de/plugins/4u/
1) Low Pass Filter 16KHz-80Hz
2)Compressor + Phat button (makes the compression more gentle), The amount does Compress + AutoGain
3)Distortion – Tube (Adds some sparkle on “top”) , Mech – Stronger Distortion
4)Master Volume
Bark of Dog – Low Frequency enhancer Plug-in