Here's a repeatable texture that resembles a light green concrete wall or something similar.
Source V. Hartikainen
A large pattern with funky shapes and form. An original. Sort of origami-ish.
Source Luuk van Baars
A dark brown fabric-like background texture with seamless pattern of winding stripes.
Source V. Hartikainen
Prismatic Geometric Pattern Background 2
Source GDJ
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay
Abstract Ellipses Background Grayscale
Source GDJ
Inspired by a design found in 'Konstantinápolyi emlékeim', Miklos Chriszto, 1893.
Source Firkin
From a drawing in 'Bond Slaves. The story of a struggle.', Isabella Varley, 1893.
Source Firkin
A seamless pattern formed from a tile made from page ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Derived from a drawing in 'Elfrica. An historical romance of the twelfth century', Charlotte Boger, 1885
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Similar to original, but without gaps in between the arrows. This seamless pattern was created from a rectangular tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Square design drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Same classic 45-degree pattern, dark version.
Source Luke McDonald
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