This background pattern contains a seamless texture of bark. It's not very realistic, but I think it looks quite nice.
Source V. Hartikainen
A seamless web texture of "green stone".
Source V. Hartikainen
Seamless Green Tile Background
Source V. Hartikainen
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Seamless pattern the basic tile for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Light gray version of the Binding pattern that looks a bit like fabric.
Source Newbury
Dark, lines, noise, tactile. You get the drift.
Source Anatoli Nicolae
Vector version of a JPG that was uploaded to Pixabay by theasad121
Source Firkin
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
Green Web Background, Seamless tile.
Source V. Hartikainen
Remixed from an image on Pixabay, the original having been uploaded by darkmoon1968.
Source Firkin
Colour version that is close to the original drawing uploaded to Pixabay by pencilparker.
Source Firkin
A seamless background pattern with impressed gray dots.
Source V. Hartikainen
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
Bit of a strange name on this one, but still nice. Tiny gray square things.
Source Carlos Valdez