This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
You may use it as is, or modify it as you like.
Source V. Hartikainen
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Simple combination of stripy squares with their negatively coloured counterparts
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
This one is amazing, truly original. Go use it!
Source Viahorizon
White little knobs, coming in at 10x10px. Sweet!
Source Amos
Sharp diamond pattern. A small 24x18px tile.
Source Tom Neal
The image depicts a seamless pattern of a tortoise in tortoiseshell (hexagon).
Source Yamachem
This seamless pattern consists of a blue grid on a yellow background.
Source V. Hartikainen
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
A pale yellow background pattern with vertical stripes. The stripes are partially faded. I think this background image turned out pretty well, especially those faded stripes.
Source V. Hartikainen
Heavily remixed from a drawing that was uploaded to Pixabay by ractapopulous
Source Firkin
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Alternative colour scheme for the original floral pattern.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
A beautiful dark padded pattern, like an old classic sofa.
Source Chris Baldie
This is a seamless pattern which is derived from a flower petal image.
Source Yamachem
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
Dark, lines, noise, tactile. You get the drift.
Source Anatoli Nicolae
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin