Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Prismatic Abstract Geometric Background 4
Source GDJ
A dark background pattern/texture of a dimpled metal plate.
Source V. Hartikainen
A beautiful dark padded pattern, like an old classic sofa.
Source Chris Baldie
White circles connecting on a light gray background.
Source Mark Collins
Zero CC tileable grass texture, photographed and made by me. CC0
Source Sojan Janso
Prismatic Abstract Background Design No Black
Source GDJ
Zero CC tileable ground (#2) cracked, crackled texture, made by me. CC0
Source Sojan Janso
Inspired by a drawing in 'Kulturgeschichte', Freidrich Hellwald, 1896.
Source Firkin
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
The starting point for this was drawn on the web site steamcoded.org/PolyskelionMaker.svg
Source Firkin
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
This reminds me of Game Cube. A nice light 3D cube pattern.
Source Sander Ottens
Prismatic Hexagonalist Pattern No Background
Source GDJ
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
A repeatable image with dark background and metal grid pattern.
Source V. Hartikainen
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
A nice and simple gray stucco material. Great on its own, or as a base for a new pattern.
Source Bartosz Kaszubowski
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
If you’re sick of the fancy 3D, grunge and noisy patterns, take a look at this flat 2D brick wall.
Source Listvetra
Derived from a JPG that was uploaded to Pixabay by ractapopulous
Source Firkin
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
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