As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Abstract Geometric Background 5
Source GDJ
This is the remix of "blue wave-seigaiha".The image depicts a seamless pattern of the front upper part of Japanese five yen coin which is used currently.This design represents a rice with ripe golden ears.
Source Yamachem
Inspired by a drawing in 'Kulturgeschichte', Freidrich Hellwald, 1896.
Source Firkin
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
That’s what it is, a dark dot. Or sort of carbon looking.
Source Tsvetelin Nikolov
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I. Version with black background.
Source Firkin
Remixed from a drawing in 'Hungary. A guide book. By several authors', 1890.
Source Firkin
Light gray grunge wall with a nice texture overlay.
Source Adam Anlauf
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A heavy hitter at 400x400px, but lovely still.
Source Breezi
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Light gray paper pattern with small traces of fiber and some dust.
Source Atle Mo
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Here's a subtle marble-like background for use on websites.
Source V. Hartikainen
Fix and cc0 to get the tile this is based on.
Source SliverKnight
A dark brown fabric-like background texture with seamless pattern of winding stripes.
Source V. Hartikainen
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ