From an image on opengameart.org shared by rubberduck.
Source Firkin
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
Pattern Background, Texture, Photoshop Structure style CC0 texture.
Source Darkmoon1968
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
The classic notebook paper with horizontal stripes.
Source Are Sundnes
This light blue background pattern is quite pleasing to the eye, it consists of a tiny rough grid pattern, which is seamless by design. That's it, if you like the color, you can use this seamless pattern in a web design without making any further modifications to it.
Source V. Hartikainen
Number 2 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
One more in the line of patterns inspired by Japanese/Asian styles. Smooth.
Source Kim Ruddock
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
Classy golf-pants pattern, or crossed stripes if you will.
Source Will Monson
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby
Bit of a strange name on this one, but still nice. Tiny gray square things.
Source Carlos Valdez
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Prismatic Abstract Background Design
Source GDJ
Geometric lines are always hot, and this pattern is no exception.
Source Listvetra
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857
Source Firkin
A black tile-able background with paper-like texture.
Source V. Hartikainen
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A rusty grunge background for websites. Feel free to use it in your site's theme.
Source V. Hartikainen
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett