Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
This one could be the shirt of a golf player. Angled lines in different thicknesses.
Source Olivier Pineda
Pattern Background, Texture, Photoshop Structure style CC0 texture.
Source Darkmoon1968
A seamless pattern formed from background pattern 102
Source Firkin
A seamless marble-like texture colored in light blue.
Source V. Hartikainen
From a drawing in 'Hubert Montreuil, or the Huguenot and the Dragoon', Francisca Ouvry, 1873.
Source Firkin
Subtle scratches on a light gray background.
Source Andrey Ovcharov
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
Inspired by this, I came up with this pattern. Madness!
Source Atle Mo
Light square grid pattern, great for a “DIY projects” sort of website, maybe?
Source Rafael Almeida
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Abstract Background Design No Black
Source GDJ
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
A free background tile with a pattern of pink bump dots. This background tile is sweet! Moreover, it's designed for use as website backgrounds.
Source V. Hartikainen