An emulated “transparent” background pattern, like that of all kinds of computer graphics software.
Source AdamStanislav
Zero CC tileable moss or lichen covered stone texture, edited from pixabay. CC0
Source Sojan Janso
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
Prismatic Triangular Background Design Mark II 5
Source GDJ
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Prismatic Abstract Background Design
Source GDJ
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
A large (588x375px) sand-colored pattern for your ever-growing collection. Shrink at will.
Source Alex Tapein
Same classic 45-degree pattern, dark version.
Source Luke McDonald
From a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Remixed from a drawing in 'Analecta Eboracensia', Thomas Widdrington, 1897.
Source Firkin
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Bit of a strange name on this one, but still nice. Tiny gray square things.
Source Carlos Valdez
Derived from a drawing in 'Historiske Afhandlinger', Adolf Jorgensen, 1898.
Source Firkin
Here's a bluish gray striped background pattern for use on web sites.
Source V. Hartikainen
Seamless pattern inspired by a drawing on Pixabay. To get the tile this is formed from, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
The name alone is awesome, but so is this sweet dark pattern.
Source Federica Pelzel
I scanned a paper coffee cup. You know, in case you need it.
Source Atle Mo
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin