Dark, lines, noise, tactile. You get the drift.
Source Anatoli Nicolae
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
A dark brown fabric-like background texture with seamless pattern of winding stripes.
Source V. Hartikainen
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Prismatic Abstract Geometric Background derived from an image on Pixabay.
Source GDJ
Inspired by a drawing in 'Kulturgeschichte', Freidrich Hellwald, 1896.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
You may use it as is, or modify it as you like.
Source V. Hartikainen
Prismatic Groovy Concentric Background
Source GDJ
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
An abstract Background pattern of purple twisty patterns.
Source TikiGiki
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Prismatic Hypnotic Pattern 2 No Background
Source GDJ
The image depicts meshed silhouettes of various things.The original image is an OCAL clipart called "Enter FOSSASIA 2016 #IoT T-shirt Design Contest" uploaded by "openclipart".Thanks.
Source Yamachem
Background formed from the original with an emboss effect
Source GDJ
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo
Black & white version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ