Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Sharp but soft triangles in light shades of gray.
Source Pixeden
Zero CC tileable ground (#2) cracked, crackled texture, made by me. CC0
Source Sojan Janso
Green Web Background, Seamless tile.
Source V. Hartikainen
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
A very slick dark rubber grip pattern, sort of like the grip on a camera.
Source Sinisha
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Prismatic Curved Diamond Pattern 6 No Background
Source GDJ
Remixed from a drawing in 'A Girl in Ten Thousand', Elizabeth Meade, 1896.
Source Firkin
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
Prepared mostly as a raster in Paint.net and vectorised.
Source Firkin
The image depicts a seamless pattern of a fishnet with a plenty of fish.It may be a lucky charm for fishermen.
Source Yamachem
A seamless pattern formed from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Sharp pixel pattern looking like some sort of fabric.
Source Dmitry
New paper pattern with a slightly organic feel to it, using some thin threads.
Source Atle Mo