A seamless texture of a rough concrete surface.
Source V. Hartikainen
Crossing lines with a subtle emboss effect on a dark background.
Source Stefan Aleksić
Colour version of the original pattern inspired by the front cover of 'Old and New Paris', Henry Edwards, 1894.
Source Firkin
It looks like a polished stone surface to me. Download it for free, as always.
Source V. Hartikainen
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Here's a tile-able wood background image for use in web design.
Source V. Hartikainen
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Seamless Prismatic Quadrilateral Line Art Pattern No Background
Source GDJ
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
A seamless pattern formed from a sports car on clker.com. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
Remixed from a JPG that was uploaded to Pixabay by Osckar
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Light gray version of the Binding pattern that looks a bit like fabric.
Source Newbury
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
Alternative colour scheme for the original floral pattern.
Source Firkin
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
I love these crisp, tiny, super subtle patterns.
Source Badhon Ebrahim
This one needs to be used in small areas; you can see it repeat.
Source Luca