A free background image with a seamless texture of cardboard. This texture of cardboard looks quite realistic, especially when is actually tiled.
Source V. Hartikainen
A repeating background with dark brown stone-like texture and abstract pattern that looks like tree trunks.
Source V. Hartikainen
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
This background pattern contains worn out colorful stripes as a texture.
Source V. Hartikainen
All good things come in threes, so I give you the third in my little concrete wall series.
Source Atle Mo
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Redrawn based on a drawing in 'По Сѣверо-Западу Россіи' Konstantin Sluchevsky, 1897.
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin