From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
Colour version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
More tactile goodness. This time in the form of some rough cloth.
Source Bartosz Kaszubowski
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
ZeroCC tileabel stone granite texture, edited from pixabay. CC0
Source Sojan Janso
A seamless pattern with wide vertical stripes colored in pale yellow.
Source V. Hartikainen
We have some linen patterns here, but none that are stressed. Until now.
Source Jordan Pittman
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
The texture of this background image has some similarities with leather, and it's colored in a dark brown color. So, if you are looking for a dark brown background image for your website, this may be an option for you.
Source V. Hartikainen
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
I love these crisp, tiny, super subtle patterns.
Source Badhon Ebrahim
Little x’es, noise and all the stuff you like. Dark like a Monday, with a hint of blue.
Source Tom McArdle
Prismatic Floral Background No Black
Source GDJ
A beautiful dark padded pattern, like an old classic sofa.
Source Chris Baldie
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
From a drawing in 'Royal Ramsgate', James Simson, 1897.
Source Firkin
A set of paper filters. The base texture is generated the same way, only the compositing mode is varied.
Source Lazur URH
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
Looks like an old rug or a computer chip.
Source Patutin Sergey
Remixed from a drawing in 'Line and form", Walter Crane, 1914.
Source Firkin