Sharp diamond pattern. A small 24x18px tile.
Source Tom Neal
Prismatic Hypnotic Pattern No Background
Source GDJ
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
Prismatic Groovy Concentric Background 2
Source GDJ
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Zero CC tileable hard cover cells book texture, 4k, scanned and made by me. CC0
Source Sojan Janso
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A repeating background for websites with a texture of black groove stripes.
Source V. Hartikainen
From a drawing in 'Picturesque New Guinea', J Lindt, 1887.
Source Firkin
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim