A heavy dark gray base, some subtle noise and a 45-degree grid makes this look like a pattern with a tactile feel to it.
Source Atle Mo
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Prismatic Curved Diamond Pattern No Background
Source GDJ
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Remixed from a PNG that was uploaded to Pixabay by gingertea
Source Firkin
Plywood Web Background background image for use in web design.
Source V. Hartikainen
From a tile that can be had 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
Crossing lines with a subtle emboss effect on a dark background.
Source Stefan Aleksić
A bit strange this one, but nice at the same time.
Source Diogo Silva
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Continuing the geometric trend, here is one more.
Source Mike Warner
A seamless pattern formed from a modified version of rwwgub's tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A repeating background with dark brown stone-like texture and abstract pattern that looks like tree trunks.
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin