A seamless pattern based on a tile that can be achieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Inspired by a drawing seen in 'City of Liverpool', James Picton, 1883.
Source Firkin
A seamless pattern with a unit cell drawn as a bitmap in Paint.net and vectorized in Vector Magic.
Source Firkin
Submitted as a black pattern, I made it light and a few steps more subtle.
Source Andy
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
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
This is lovely, just the right amount of subtle noise, lines and textures.
Source Richard Tabor
This one is so simple, yet so good. And you know it. Has to be in the collection.
Source Gluszczenko
Just what the name says, paper fibers. Always good to have.
Source Heliodor jalba
A classic dark tile for a bit of vintage darkness.
Source Listvetra
Dark pattern with some nice diagonal stitched lines crossing over.
Source Ashton
Lovely pattern with splattered vintage speckles.
Source David Pomfret
A brown seamless wood texture in a form of stripe pattern. The result has turned out pretty well, in my opinion.
Source V. Hartikainen
This background pattern contains a texture of yellow wood planks. I think it looks quite original.
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
Black And White Floral Pattern Background from PDP.
Source GDJ
Zero CC bark from fur tree tileable texture, photographed and made by me. CC0
Source Sojan Janso
Remixed from a drawing in 'Prehistoric Man: researches into the origin of civilisation in the old and the new world', Daniel Wilson, 1876.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Because I love dark patterns, here is Brushed Alum in a dark coating.
Source Tim Ward
New paper pattern with a slightly organic feel to it, using some thin threads.
Source Atle Mo
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
A seamless stone-like background for blogs or any other type of websites.
Source V. Hartikainen