People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Derived from a design in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
Sometimes you just need the simplest thing.
Source Fabricio
Prismatic Curved Diamond Pattern No Background
Source GDJ
This one could be the shirt of a golf player. Angled lines in different thicknesses.
Source Olivier Pineda
Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
Prismatic Polka Dots Mark II 3 No Background
Source GDJ
You know you can’t get enough of these linen-fabric-y patterns.
Source James Basoo
A seamless light gray paper texture with horizontal double lines.
Source V. Hartikainen
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
A series of 5 patterns. That’s what the P stands for, if you didn’t guess it.
Source Dima Shiper
CC0 and seamless wellington boot pattern.
Source SliverKnight
A seamless pattern with wide vertical stripes colored in pale yellow.
Source V. Hartikainen
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
Remixed from a drawing in 'Hungary. A guide book. By several authors', 1890.
Source Firkin
The image depicts polka dot seamless pattern.
Source Yamachem
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A seamless background texture of old cardboard.
Source V. Hartikainen
The image a seamless pattern derived from a weed which I can't identify.The original weed image is from here:https://jp.pinterest.com/pin/500744052301423641/
Source Yamachem
This was formed by distorting an image of a background on Pixabay.
Source Firkin