Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
A version without colours blended together to give a different look.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Pattern Background, Texture, Photoshop Structure style CC0 texture.
Source Darkmoon1968
From a drawing in 'Picturesque New Guinea', J Lindt, 1887.
Source Firkin
Prismatic Groovy Concentric Background 3
Source GDJ
The edges of all the red objects line up either vertically or horizontally, but it doesn't appear so. Made from a square tile that can be got by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Prismatic Geometric Pattern Background
Source GDJ
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
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
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
This one is amazing, truly original. Go use it!
Source Viahorizon
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Derived from a drawing in 'Elfrica. An historical romance of the twelfth century', Charlotte Boger, 1885
Source Firkin
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
Tiny, tiny 3D cubes. Reminds me of the good old pattern from k10k.
Source Etienne Rallion
All good things come in threes, so I give you the third in my little concrete wall series.
Source Atle Mo
There are many carbon patterns, but this one is tiny.
Source Designova
A rusty grunge background for websites. Feel free to use it in your site's theme.
Source V. Hartikainen
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin