Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
Medium gray fabric pattern with 45-degree lines going across.
Source Atle Mo
A large pattern with funky shapes and form. An original. Sort of origami-ish.
Source Luuk van Baars
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
This background pattern contains a texture of yellow wood planks. I think it looks quite original.
Source V. Hartikainen
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Abstract Tiled Background Extended 8
Source GDJ
Inspired by a drawing in 'Kulturgeschichte', Freidrich Hellwald, 1896.
Source Firkin
Here's a new background image for websites with a seamless pink texture. It should look beautiful with website themes where light pink background is needed. The background is seamless, therefore it should be used as a tiled background.
Source V. Hartikainen
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Nasty or not, it’s a nice pattern that tiles. Like they all do.
Source Badhon Ebrahim
From a drawing in 'Hubert Montreuil, or the Huguenot and the Dragoon', Francisca Ouvry, 1873.
Source Firkin
Green Web Background, Seamless tile.
Source V. Hartikainen
A seamless pattern with green and yellow diagonal lines on top of a white dotted background.
Source V. Hartikainen
Actually remixed from a pattern on Pixabay. But then noticed a very similar one on Openclipart.org uploaded by btj51q2.
Source Firkin
The name alone is awesome, but so is this sweet dark pattern.
Source Federica Pelzel
A free seamless background pattern for use on websites.
Source V. Hartikainen
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
A re-make of the Gradient Squares pattern.
Source Dimitar Karaytchev
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
Pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin