Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
Zero CC tileable hard cover red book, scanned and made by me. CC0
Source Sojan Janso
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Formed from decorative divider 184 in paint.net. Vectorised with Vector Magic.
Source Firkin
Derived from an image that was uploaded to Pixabay by starchim01
Source Firkin
Fix and cc0 to get the tile this is based on.
Source SliverKnight
This is a seamless pattern which is derived from a flower petal image.
Source Yamachem
This is the remix of "Tileable Wave Pattern 2" uploaded by "Arvin61r58".Thanks.I added a wire-mesh fence seamless pattern as a lower layer.
Source Yamachem
Detailed but still subtle and quite original. Lovely gray shades.
Source Kim Ruddock
A seamless pattern formed from background pattern 102
Source Firkin
A gray background pattern with a texture of textile. Suits perfectly for web design.
Source V. Hartikainen
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
White fabric looking texture with some nice random wave features.
Source Hendrik Lammers
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
I love the movie Pineapple Express, and I’m also liking this Pineapple right here.
Source Audee Mirza
Background pattern originally a PNG drawn in Paint.net
Source Firkin
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc