Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
Here's a brown background pattern with subtle stripes. I hope you'll like the color. If not, feel free to change it using an image editor, if you know how of course. Personally, I'm using GIMP to create these backgrounds.
Source V. Hartikainen
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
The file was named striped lens, but hey – Translucent Fibres works too.
Source Angelica
A seamless pattern formed from a sports car on clker.com. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
This background has abstract texture with some similarities to wood.
Source V. Hartikainen
Embossed lines and squares with subtle highlights.
Source Alex Parker
A gray background pattern with a texture of textile. Suits perfectly for web design.
Source V. Hartikainen
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
A yellow tiled background... Blurriness, bokeh effect and rectangles pattern in one mix.
Source V. Hartikainen
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Wasn't satisfied with the original's colouring. Too much component transfer and colormatrixes yet the results are lacking a bit. So this time it is a simple black to transparent fade, making it possible remixing easily once there will be other blending modes supported as well. Probably in inkscape 0.92.
Source Lazur URH
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
8 by 8 pixels, and just what the title says.
Source pixilated
The classic notebook paper with horizontal stripes.
Source Are Sundnes
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
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