It looks like a polished stone surface to me. Download it for free, as always.
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
Medium gray fabric pattern with 45-degree lines going across.
Source Atle Mo
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
An abstract Background pattern of purple twisty patterns.
Source TikiGiki
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ
This was formed by distorting an image of a background on Pixabay.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
From a drawing in 'Prose and Verse ', William Linton, 1836.
Source Firkin
A floral background formed from numerous clones of flower 117.
Source Firkin
A hint of orange color, and some crossed and embossed lines.
Source Adam Anlauf
Zero CC tileable bark texture, photographed and made by me. CC0
Source Sojan Janso
Remixed from a drawing in 'Some account of the Worshipful Company of Ironmongers', John Nicholl, 1866.
Source Firkin
More in the paper realm, this time with fibers.
Source Jorge Fuentes
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Remixed from a drawing in 'Works. Popular edition', John Ruskin, 1886.
Source Firkin
Seamless pattern formed from a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
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
One more in the line of patterns inspired by Japanese/Asian styles. Smooth.
Source Kim Ruddock
This is a remix of "blue wave-seigaiha".I hope this subtle color version of Seigaiha would be suitable for background .
Source Yamachem
Derived from an image that was uploaded to Pixabay by TheDigitalArtist
Source Firkin
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin