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
Hey, you never know when you’ll need a bird pattern, right?
Source Pete Fecteau
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
These dots are already worn for you, so you don’t have to.
Source Matt McDaniel
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
This seamless pattern consists of a blue grid on a yellow background.
Source V. Hartikainen
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
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 could be the shirt of a golf player. Angled lines in different thicknesses.
Source Olivier Pineda
Prismatic Triangular Background Design Mark II 5
Source GDJ
The image depicts meshed silhouettes of various things.The original image is an OCAL clipart called "Enter FOSSASIA 2016 #IoT T-shirt Design Contest" uploaded by "openclipart".Thanks.
Source Yamachem
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Background pattern originally a PNG drawn in Paint.net
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen