To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
Vertical lines with a bumpy, yet crisp, feel to it.
Source Raasa
A yellow tiled background... Blurriness, bokeh effect and rectangles pattern in one mix.
Source V. Hartikainen
A seamless web texture with illustration of pale color stains on canvas.
Source V. Hartikainen
From a drawing in 'Royal Ramsgate', James Simson, 1897.
Source Firkin
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
A seamless web background with texture of aged grid paper.
Source V. Hartikainen
I’m starting to think I have a concrete wall fetish.
Source Atle Mo
Prismatic Geometric Tessellation Pattern No Background
Source GDJ
Lovely pattern with splattered vintage speckles.
Source David Pomfret
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
Lovely pattern with some good-looking non-random noise lines.
Source Zucx
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin