Based on several public domain drawings on Wikimedia Commons. This was formed from a rectangular tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Derived from a drawing in 'Historiske Afhandlinger', Adolf Jorgensen, 1898.
Source Firkin
This light yellow background pattern consists of an irregular pattern of spots. Here's a light background pattern with yellowish tint.
Source V. Hartikainen
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
From a drawing in 'Hyde Park from Domesday-Book to date', John Ashton, 1896.
Source Firkin
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
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Prismatic Groovy Concentric Background 4
Source GDJ
Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
This ladies and gentlemen, is texturetastic! Love it.
Source Adam Pickering
A seamless pattern formed from a tile made from page ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Awesome name, great pattern. Who does not love space?
Source Nick Batchelor
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.
Source Nathan Spady
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Psychedelic Geometric Background No Black
Source GDJ
Prismatic Geometric Pattern Background 2
Source GDJ
It’s a hole, in a pattern. On your website. Dig it!
Source Josh Green
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
This seamless pattern consists of a blue grid on a yellow background.
Source V. Hartikainen
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin