From an image on opengameart.org shared by rubberduck.
Source Firkin
Prismatic Abstract Geometric Background 4
Source GDJ
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
Remixed from an image on Pixabay uploaded by Prawny
Source Firkin
Use shift+alt+i on the selected rectangle in Inkscape to get the tile this is based on
Source Firkin
There are many carbon patterns, but this one is tiny.
Source Designova
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
ZeroCC tileable beechwood wood texture, generated in Neo Texture Edit by me. CC0
Source Sojan Janso
Pattern Background, Texture, Photoshop Structure style CC0 texture.
Source Darkmoon1968
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
Retro Circles Background 4 No Black
Source GDJ
Has nothing to do with toast, but it’s nice and subtle.
Source Pippin Lee
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Prismatic Hypnotic Pattern No Background
Source GDJ
A large pattern with funky shapes and form. An original. Sort of origami-ish.
Source Luuk van Baars
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Derived from an image that was uploaded to Pixabay by TheDigitalArtist
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin