From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin
Lovely pattern with some good-looking non-random noise lines.
Source Zucx
A free background image with a seamless texture of cardboard. This texture of cardboard looks quite realistic, especially when is actually tiled.
Source V. Hartikainen
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
Retro Circles Background 5 No Black
Source GDJ
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
Zero CC tileable seed texture, edited by me to be seamless from a Pixabay image. CC0
Source Sojan Janso
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Prismatic 3D Isometric Tessellation Pattern 6
Source GDJ
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
From a drawing in 'Codogno e il suo territorio nella cronaca e nella storia'', Gio and Giarella Cairo, 1897.
Source Firkin
Paper pattern with small dust particles and 45-degree strokes.
Source Atle Mo
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Remixed from a drawing in 'Jezebel's Daughter', Wilkie Collins 1880
Source Firkin