People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
This was formed by distorting an image of a background on Pixabay.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
A seamless pattern with wide vertical stripes colored in pale yellow.
Source V. Hartikainen
Not sure if this is related to the Nami you get in Google image search, but hey, it’s nice!
Source Dertig Media
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
A green background pattern with warped vertical stripes and a grunge look.
Source V. Hartikainen
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
More in the paper realm, this time with fibers.
Source Jorge Fuentes
Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
Based on several public domain drawings on Wikimedia Commons. This was formed from a rectangular tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i
Source Firkin
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
On a large canvas you can see it tiling, but used on smaller areas, it’s beautiful.
Source Paul Phönixweiß
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin