To get the repeating unit, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Seamless Prismatic Geometric Pattern With Background
Source GDJ
A pattern derived from part of a fractal rendering in Paint.net.
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
Fake or not, it’s quite luxurious.
Source Factorio.us Collective
A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
I asked Gjermund if he could make a pattern for us – result!
Source Gjermund Gustavsen
Might not be super subtle, but quite original in its form.
Source Alex Smith
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
A seamless marble-like texture colored in light blue.
Source V. Hartikainen
A simple but elegant classic. Every collection needs one of these.
Source Christopher Burton
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
A seamless pattern recreated from an image on Pixabay. It is reminiscent of parquet flooring and is formed from a square tile, which can be recovered in Inkscape by selecting the ungrouped rectangle and using shift-alt-I together.
Source Firkin
Number 4 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
8 by 8 pixels, and just what the title says.
Source pixilated
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Abstract Ellipses Background Grayscale
Source GDJ
Actually remixed from a pattern on Pixabay. But then noticed a very similar one on Openclipart.org uploaded by btj51q2.
Source Firkin
You guessed it – looks a bit like cloth.
Source Peax Webdesign
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
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo