An abstract texture of water. It's not perfect, but will do. You may download if you like it.
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
By popular request, an outline version of the pentagon pattern.
Source Atle Mo
Gold Triangular Seamless Pattern No Background
Source GDJ
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
A hint of orange color, and some crossed and embossed lines.
Source Adam Anlauf
Sharp pixel pattern looking like some sort of fabric.
Source Dmitry
ZeroCC tileable wood boards texture, photographed and made by me. CC0
Source Sojan Janso
Prismatic Curved Diamond Pattern No Background
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
More in the paper realm, this time with fibers.
Source Jorge Fuentes
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Light gray version of the Binding pattern that looks a bit like fabric.
Source Newbury
The image depicts a seamless pattern made using a bird's face.
Source Yamachem
We have some linen patterns here, but none that are stressed. Until now.
Source Jordan Pittman
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
Remixed from a drawing in 'A Child of the Age', Francis Adams, 1894.
Source Firkin
A dark background pattern/texture of a dimpled metal plate.
Source V. Hartikainen
A light gray background pattern with seamless fabric-like texture and almost unnoticeable stripes.
Source V. Hartikainen
Zero CC tileable hard cover green book, scanned and made by me. CC0
Source Sojan Janso
This background texture resembles stone. It may be used as a background on web pages or on some of their html elements (header, borders, menu bar, etc.). Just modify it for your needs.
Source V. Hartikainen
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin