Definitely Eevee Materials System For Blender 2.9 Free Download
It’s a collection of 100+ EEVEE compatible photoreal Materials which can be added to any object using the included FREE version of KIT OPS. No UV mapping necessary for objects!
Using the included systematized approach, you can create an infinite number of derivative photoreal materials.
Plus there is the Amazing Dirt Group Node, which adds altitude mapped and ambient occlusion dirt to any material.
While the materials can be “appended” via Blender 2.8, the System comes complete with 7 courses walking you through how best to install and use the Materials and the System.