Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
Dead simple but beautiful horizontal line pattern.
Source Fabian Schultz
A free background pattern with abstract green tiles.
Source V. Hartikainen
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
Remixed from a raster on Pixabay, that was uploaded by ArtsyBee.
Source Firkin
This is lovely, just the right amount of subtle noise, lines and textures.
Source Richard Tabor
The Grid. A digital frontier. I tried to picture clusters of information as they traveled through the computer.
Source Haris Šumić
A smooth mid-tone gray, or low contrast if you will, linen pattern.
Source Jordan Pittman
CC0 remixed from a drawing. Walter Crane, 1914, Firkin.
Source SliverKnight
A seamless pattern recreated from an image on Pixabay. It is reminiscent of parquet flooring and is formed from a square tile, which can be recovered in Inkscape by selecting the ungrouped rectangle and using shift-alt-I together.
Source Firkin
The tile this fill pattern is based on can be had by using shift+alt+i on the rectangle.
Source Firkin
Remixed from a raster on Pixabay that was uploaded by ArtsyBee.
Source Firkin
ZeroCC tileable beechwood wood texture, generated in Neo Texture Edit by me. CC0
Source Sojan Janso
Some dark 45 degree angles creating a nice pattern. Huge.
Source Dark Sharp Edges
Prismatic Geometric Pattern Background No Black
Source GDJ
Some rectangles, a bit of dust and grunge, plus a hint of concrete.
Source Atle Mo
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male