A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
Another fairly simple design drawn in Paint.net and vectorized in Inkscape.
Source Firkin
Black & white version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Colour version that is close to the original drawing uploaded to Pixabay by pencilparker.
Source Firkin
This one is amazing, truly original. Go use it!
Source Viahorizon
Derived from an image that was uploaded to Pixabay by darkmoon1968
Source Firkin
A dark pattern made out of 3×3 circles and a 1px shadow. This works well as a carbon texture or background.
Source Atle Mo
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Prismatic Geometric Pattern Background No Black
Source GDJ
Prismatic Abstract Background Design
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A seamless pattern formed from background pattern 102
Source Firkin
Abstract Ellipses Background Grayscale
Source GDJ
This background pattern has futuristic look. So, maybe it could be used on websites or blogs dedicated to video games?!
Source V. Hartikainen
Lovely pattern with splattered vintage speckles.
Source David Pomfret
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
White circles connecting on a light gray background.
Source Mark Collins
A seamless background tile of aged paper with shabby look.
Source V. Hartikainen
From an image on opengameart.org shared by rubberduck.
Source Firkin
Heavily remixed from a drawing that was uploaded to Pixabay by ractapopulous
Source Firkin