A very nice surprise from Blender Institute, with a substantial collection of textures. All for free, released (and shared) under CCO license - similar to public domain, free to use for any purpose. Source and library are there.
The original release notes reads as below .
Welcome to this curated collection of Blender Institute textures and image resources. This collection is an on-going project, as with each project we create a number of textures based on our own resources (photographs, scans, etc.) or made completely from scratch. At the moment you can find all the textures from the past Open Projects that were considered re-usable.
People who have contributed to these textures:
Andrea Weikert, Andy Goralczyk, Basse Salmela, Ben Dansie, Campbell Barton, Enrico Valenza, Ian Hubert, Kjartan Tysdal, Manu Järvinen, Massimiliana Pulieso, Matt Ebb, Pablo Vazquez, Rob Tuytel, Roland Hess, Sarah Feldlaufer, Sönke Mäter
This collection is available as CC0 - similar to public domain, free to use for any purpose.
Thank you Blender Institute / Blender Cloud.