A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Actually remixed from a pattern on Pixabay. But then noticed a very similar one on Openclipart.org uploaded by btj51q2.
Source Firkin
One more brick pattern. A bit more depth to this one.
Source Benjamin Ward
This is a seamless pattern of regular hexagon which has a honeycomb structure.
Source Yamachem
Retro Circles Background 5 No Black
Source GDJ
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
The starting point for this was drawn on the web site steamcoded.org/PolyskelionMaker.svg
Source Firkin
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
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Black brick wall pattern. Brick your site up!
Source Alex Parker
Three shades of gray makes this pattern look like a small carbon fiber surface. Great readability even for small fonts.
Source Atle Mo
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Green Background Pattern
Source V. Hartikainen
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Snowflakes Pattern No Background
Source GDJ
We have some linen patterns here, but none that are stressed. Until now.
Source Jordan Pittman
Here's an yet another seamless note paper texture for use as a background on websites.
Source V. Hartikainen
There are many carbon patterns, but this one is tiny.
Source Designova