A pattern derived from part of a fractal rendering in Paint.net.
Source Firkin
The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Here's an yet another background for websites, with a seamless texture of wood planks this time.
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
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
Same as the black version, but now in shades of gray. Very subtle and fine grained.
Source Atle Mo
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Derived from a JPG that was uploaded to Pixabay by ractapopulous
Source Firkin
Horizontal and vertical lines on a light gray background.
Source Adam Anlauf
Horizontal and vertical lines on a light gray background.
Source Adam Anlauf
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
Pattern Background, Texture, Photoshop Structure style CC0 texture.
Source Darkmoon1968
Green Background Pattern
Source V. Hartikainen
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Prismatic Abstract Background Design No Black
Source GDJ
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
A blue background wallpaper for websites. It has a seamless texture with vertical stripes. It looks quite nice not only when using as a tiled background on websites, but also on computer desktops.
Source V. Hartikainen
An emulated “transparent” background pattern, like that of all kinds of computer graphics software.
Source AdamStanislav