A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
A seamless stone-like background for blogs or any other type of websites.
Source V. Hartikainen
The name is totally random, but hey, it sounds good.
Source Atle Mo
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
A new take on the black linen pattern. Softer this time.
Source Atle Mo
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868.
Source Firkin
Prismatic Geometric Pattern Background
Source GDJ
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
A seamless pattern with a unit cell drawn as a bitmap in Paint.net and vectorized in Vector Magic.
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
Kaleidoscope Prismatic Abstract No Background
Source GDJ
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
A cute x, if you need that sort of thing.
Source Juan Scrocchi
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Nicely executed tiling for an interesting pattern.
Source Ignasi Àvila Padró