You guessed it – looks a bit like cloth.
Source Peax Webdesign
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Prismatic Groovy Concentric Background 4
Source GDJ
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
Light and tiny, just the way you like it.
Source Rohit Arun Rao
Pattern Background, Texture, Photoshop Structure style CC0 texture.
Source Darkmoon1968
A seamless background pattern of dark brown wood planks.
Source V. Hartikainen
Prismatic Polka Dots Mark II No Background
Source GDJ
Light gray version of the Binding pattern that looks a bit like fabric.
Source Newbury
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
A dark metallic background with a pattern of stamped dots. Here's a dark "metallic" background pattern for you.
Source V. Hartikainen
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin