A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
A pattern formed from repeated instances of corner decoration 8. To get the basic tile select the rectangle in Inkscape and use shift+alt+i
Source Firkin
A seamless light gray paper texture with horizontal double lines.
Source V. Hartikainen
Pattern Background, Texture, Photoshop Structure style CC0 texture.
Source Darkmoon1968
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Sometimes you just need the simplest thing.
Source Fabricio
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
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
The name alone is awesome, but so is this sweet dark pattern.
Source Federica Pelzel
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Prismatic Floral Background No Black
Source GDJ
The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin