Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Submitted as a black pattern, I made it light and a few steps more subtle.
Source Andy
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo
Fake or not, it’s quite luxurious.
Source Factorio.us Collective
It looks very nice I think.
Source V. Hartikainen
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
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
Beautiful dark noise pattern with some dust and grunge.
Source Vincent Klaiber
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
The tile can be had by using shift+alt+i on the selected rectangle in Inkscape
Source Firkin
The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin