From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
A black tile-able background with paper-like texture.
Source V. Hartikainen
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
Prismatic Chevrons Pattern 5 With Background
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
A comeback for you: the popular Escheresque, now in black.
Source Patten
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Just like the black maze, only in light gray. Duh.
Source Peax
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
As simple and subtle as it gets. But sometimes that’s just what you want.
Source Designova
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
He influenced us all. “Don’t be sad because it’s over. Smile because it happened.”
Source Atle Mo
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Number 1 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
I skipped number 3, because it wasn’t all that great. Sorry.
Source Dima Shiper
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Nothing like a clean set of bed sheets, huh?
Source Badhon Ebrahim
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
Zero CC tileable seed texture, edited by me to be seamless from a Pixabay image. CC0
Source Sojan Janso