A seamless pattern formed from a square tile based on a jpg on Pixabay. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Sharp but soft triangles in light shades of gray.
Source Pixeden
A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
On a large canvas you can see it tiling, but used on smaller areas, it’s beautiful.
Source Paul Phönixweiß
ZeroCC tileable stone texture, edited from pixabay, CC0
Source Sojan Janso
Geometric triangles seem to be quite hot these days.
Source Pixeden
Zero CC bark from fur tree tileable texture, photographed and made by me. CC0
Source Sojan Janso
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
An emulated “transparent” background pattern, like that of all kinds of computer graphics software.
Source AdamStanislav
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Abstract Tiled Background Extended 6
Source GDJ
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
Prismatic Rounded Squares Grid 4 No Background
Source GDJ
A yellow tiled background... Blurriness, bokeh effect and rectangles pattern in one mix.
Source V. Hartikainen