CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Zero CC tileable dry grass texture, photographed and made by me. CC0
Source Sojan Janso
I love these crisp, tiny, super subtle patterns.
Source Badhon Ebrahim
Similar to original, but without gaps in between the arrows. This seamless pattern was created from a rectangular tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Remixed from a drawing in 'Incidents on a Journey through Nubia to Darfoor', F. Ensor, 1891.
Source Firkin
Abstract Stars Geometric Pattern Prismatic No Background
Source GDJ
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
Prismatic Groovy Concentric Background No Black
Source GDJ
From an image on opengameart.org shared by rubberduck.
Source Firkin
The act or state of corrugating or of being corrugated, a wrinkle; fold; furrow; ridge.
Source Anna Litvinuk
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
Might not be super subtle, but quite original in its form.
Source Alex Smith
Super dark, crisp and detailed. And a Kill Bill reference.
Source Badhon Ebrahim
Remixed from a drawing in 'Canadian forest industries July-December', 1915
Source Firkin