The image is a seamless pattern of a fishnet.
Source Yamachem
Used correctly, this could be nice. Used in a bad way, all hell will break loose.
Source Atle Mo
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
A white version of the very popular linen pattern.
Source Ant Ekşiler
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A black tile-able background with paper-like texture.
Source V. Hartikainen
Hexagonal dark 3D pattern. What more can you ask for?
Source Norbert Levajsics
From a drawing in 'Worsborough; its historical associations and rural attractions', Joseph Wilkinson, 1879.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Here's an yet another background for websites, with a seamless texture of wood planks this time.
Source V. Hartikainen
Orange-red pattern for tiled backgrounds.
Source V. Hartikainen
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
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
From a drawing in 'Hyde Park from Domesday-Book to date', John Ashton, 1896.
Source Firkin
Remixed from a drawing in 'Analecta Eboracensia', Thomas Widdrington, 1897.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Remixed from a drawing that was uploaded to Pixabay by captenpub.
Source Firkin
This light background pattern has a texture of "frozen" surface with diagonal stripes. Here's an yet another addition to the collection of free website backgrounds.
Source V. Hartikainen