A comeback for you: the popular Escheresque, now in black.
Source Patten
The original enhanced with some gradients.
Source Firkin
A seamless pattern with a unit cell drawn as a bitmap in Paint.net and vectorized in Vector Magic.
Source Firkin
Prismatic Abstract Line Art Pattern Background 2
Source GDJ
Remixed from a drawing in 'A Child of the Age', Francis Adams, 1894.
Source Firkin
Medium gray fabric pattern with 45-degree lines going across.
Source Atle Mo
A seamless web texture with illustration of pale color stains on canvas.
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
A pattern drawn in Paint.net and vectorized in Inkscape.
Source Firkin
A comeback for you: the popular Escheresque, now in black.
Source Patten
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
Background formed from the original with an emboss effect
Source GDJ
Remixed from a raster on Pixabay that was uploaded by ArtsyBee.
Source Firkin
A background pattern with blue on white vertical stripes.
Source V. Hartikainen
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Remixed from an image on Pixabay, the original having been uploaded by darkmoon1968.
Source Firkin
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A bit like some carbon, or knitted netting if you will.
Source Anna Litvinuk