The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
From a drawing in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
A seamless pattern formed from a sports car on clker.com. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
A free background pattern with abstract green tiles.
Source V. Hartikainen
The file was named striped lens, but hey – Translucent Fibres works too.
Source Angelica
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
Classic vertical lines, in all its subtlety.
Source Cody L
Here's an yet another background for websites, with a seamless texture of wood planks this time.
Source V. Hartikainen
There are many carbon patterns, but this one is tiny.
Source Designova
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868
Source Firkin
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
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
Did some testing with Repper Pro tonight, and this gray mid-tone pattern came out.
Source Atle Mo
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
Prismatic Abstract Geometric Background 2 No Black
Source GDJ