Might not be super subtle, but quite original in its form.
Source Alex Smith
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
White handmade paper pattern with small bumps.
Source Marquis
From a drawing in 'Two Women in the Klondike', Mary Hitchcock, 1899.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Zero CC tileable hard cover red book, scanned and made by me. CC0
Source Sojan Janso
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Prismatic Groovy Concentric Background 5
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
Prismatic Abstract Background Design No Black
Source GDJ
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
From a drawing in 'Worsborough; its historical associations and rural attractions', Joseph Wilkinson, 1879.
Source Firkin
Prismatic Abstract Background Design
Source GDJ
Subtle scratches on a light gray background.
Source Andrey Ovcharov
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio