As simple and subtle as it gets. But sometimes that’s just what you want.
Source Designova
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
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
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Abstract Tiled Background Extended 12
Source GDJ
A dark gray, sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Just the symbols of the signs of the zodiac distributed in a chequer board-like pattern
Source Firkin
As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
Remixed from a drawing in 'Очерки Русской Исторіи въ памятникахъ быта', Petr Polevoi, 1879.
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
A repeating background of beige paper with vintage look. Repeats to infinity, as usual.
Source V. Hartikainen
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Inspired by a JPG that was uploaded to Pixabay by kokon_art
Source Firkin
Sweet and subtle white plaster with hints of noise and grunge.
Source Phil Maurer
The image depicts a seamless pattern of pine tree leaves.
Source Yamachem
Seamless Green Tile Background
Source V. Hartikainen
A free seamless background pattern for use on websites.
Source V. Hartikainen
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin