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
Zero CC tileable yellow craft paper; scanned and made by me. CC0
Source Sojan Janso
Prismatic Hexagonalist Pattern No Background
Source GDJ
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
To get the repeating unit, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
This is the remix of an OCAL clipart called "Art Nouveau ornament" uploaded by "microcosme".Thanks.This is a seamless pattern of an Art Nouveau ornament.
Source Yamachem
Remixed from a drawing in 'Line and form", Walter Crane, 1914.
Source Firkin
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
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
Derived from a JPG that was uploaded to Pixabay by ractapopulous
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
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A comeback for you: the popular Escheresque, now in black.
Source Patten
Derived from an image that was uploaded to Pixabay by darkmoon1968
Source Firkin
Prismatic Groovy Concentric Background 3
Source GDJ
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Zero CC tileable moss or lichen covered stone texture, edited from pixabay. CC0
Source Sojan Janso
Thin lines, noise and texture creates this crisp dark denim pattern.
Source Marco Slooten