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
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
Feel free to use this seamless background texture as a background on a web site. It's colored in a light pink color and is seamlessly tile-able.
Source V. Hartikainen
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
A repeatable image with dark background and metal grid pattern.
Source V. Hartikainen
ZeroCC tileable mossy (lichen) stone texture, edited from pixabay. CC0
Source Sojan Janso
A bit simplified version. Although it could be edited out to be simpler. Anyway, this time the tiling is converted to a pattern fill -which is using clipping for the tile's edges.
Source Lazur URH
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
Classic vertical lines, in all its subtlety.
Source Cody L
Light square grid pattern, great for a “DIY projects” sort of website, maybe?
Source Rafael Almeida
Lovely pattern with splattered vintage speckles.
Source David Pomfret
A seamless pale yellow paper background with a pattern of animal tracks.
Source V. Hartikainen
The starting point for this was a texture drawn with the 'Radial Colors' plug-in in Paint.net.
Source Firkin
Remixed from an image on Pixabay uploaded by Prawny
Source Firkin
This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
He influenced us all. “Don’t be sad because it’s over. Smile because it happened.”
Source Atle Mo
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees