CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Derived from a PNG that was uploaded to Pixabay by nutkitten
Source Firkin
A free grid paper background pattern for using on web sites.
Source V. Hartikainen
Colourful background achieved with gradient fills.
Source Firkin
More bright luxury. This is a bit larger than fancy deboss, and with a bit more noise.
Source Viszt Péter
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo
Zero CC tillable hard cover red book with X shape marks. Scanned and made by me.
Source Sojan Janso
Background Wall, Art Abstract, Star Well & CC0 texture.
Source Ractapopulous
Abstract Ellipses Background Grayscale
Source GDJ
A nice and simple gray stucco material. Great on its own, or as a base for a new pattern.
Source Bartosz Kaszubowski
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Gold Triangular Seamless Pattern No Background
Source GDJ
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
A seamless background texture of old cardboard.
Source V. Hartikainen
Zero CC tileable bark texture, photographed and made by me. CC0
Source Sojan Janso
Sharp but soft triangles in light shades of gray.
Source Pixeden
Paper model of a tetrahedron. Modelo de papel de um tetraedro.
Source laobc
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler