People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
Prismatic Geometric Tessellation Pattern No Background
Source GDJ
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Submitted by DomainsInfo – wtf, right? But hey, a free pattern.
Source DomainsInfo
Remixed from a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
This was submitted in a beige color, hence the name. Now it’s a gray paper pattern.
Source Konstantin Ivanov
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
One can never have too few rice paper patterns, so here is one more.
Source Atle Mo
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
Colorful Floral Background No Black
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Prismatic Abstract Geometric Background 5
Source GDJ
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
On a large canvas you can see it tiling, but used on smaller areas, it’s beautiful.
Source Paul Phönixweiß
Might not be super subtle, but quite original in its form.
Source Alex Smith
ZeroCC tileable wood boards texture, photographed and made by me. CC0
Source Sojan Janso
A seamless background pattern with impressed gray dots.
Source V. Hartikainen
You know, tiny and sharp. I’m sure you’ll find a use for it.
Source Atle Mo
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen