Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
Might not be super subtle, but quite original in its form.
Source Alex Smith
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Some rectangles, a bit of dust and grunge, plus a hint of concrete.
Source Atle Mo
Prismatic Abstract Line Art Pattern Background 2
Source GDJ
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
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
An abstract texture of water. It's not perfect, but will do. You may download if you like it.
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The texture of this background image has some similarities with leather, and it's colored in a dark brown color. So, if you are looking for a dark brown background image for your website, this may be an option for you.
Source V. Hartikainen
Can never have too many knitting patterns, especially as nice as this.
Source Victoria Spahn
Zero CC tileable moss or lichen covered stone texture, edited from pixabay. CC0
Source Sojan Janso
White circles connecting on a light gray background.
Source Mark Collins
Prismatic Hexagonalist Pattern No Background
Source GDJ
Looks like an old rug or a computer chip.
Source Patutin Sergey
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
This was formed by distorting an image of a background on Pixabay.
Source Firkin
A classic dark tile for a bit of vintage darkness.
Source Listvetra
Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
Prismatic Abstract Geometric Background derived from an image on Pixabay.
Source GDJ
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin