From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
The following repeating website background is colored in a blue gray color and resembles a concrete wall or something similar to it.
Source V. Hartikainen
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
From a drawing in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
Here's a seamless brown cork board background texture. Feel free to download or reshare if you like.
Source V. Hartikainen
Prismatic Polka Dots 3 No Background
Source GDJ
An abstract texture of black metal pipes (seamless).
Source V. Hartikainen
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
The file was named striped lens, but hey – Translucent Fibres works too.
Source Angelica
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
Colour version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
From a drawing in 'Royal Ramsgate', James Simson, 1897.
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin