Horizontal and vertical lines on a light gray background.
Source Adam Anlauf
Remixed from an image on Pixabay uploaded by Prawny
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A dark metallic background with a pattern of stamped dots. Here's a dark "metallic" background pattern for you.
Source V. Hartikainen
Here's a dark background pattern that contains a steel grid pattern as a texture. Use it as a website background or for other purposes. It's free!
Source V. Hartikainen
This is a remix of "geometrical pattern 01".
Source Yamachem
Remixed from a PNG that was uploaded to Pixabay by gingertea
Source Firkin
Remixed from a PNG that was uploaded to Pixabay by k_jprather
Source Firkin
Prismatic Abstract Line Art Pattern Background
Source GDJ
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
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
The original has been presented as black on transparent and stored in the pattern definitions. To retrieve the unit tile select the rectangle in Inkscape and use shift+alt+i
Source Firkin
It looks like a polished stone surface to me. Download it for free, as always.
Source V. Hartikainen
Prismatic Abstract Geometric Background 5
Source GDJ
Prismatic Triangular Background Design Mark II 5
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin