This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Prismatic Curved Diamond Pattern 2 No Background
Source GDJ
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
8 by 8 pixels, and just what the title says.
Source pixilated
Number 1 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Greyscale version of a pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
From a drawing in 'La Principauté de Liège et les Pays-Bas au XVIe siècle', Société des Bibliophiles Liégeois ,1887.
Source Firkin
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
ZeroCC tileable mossy (lichen) stone texture, edited from pixabay. CC0
Source Sojan Janso
Submitted as a black pattern, I made it light and a few steps more subtle.
Source Andy
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Simple combination of stripy squares with their negatively coloured counterparts
Source Firkin
Seamless Prismatic Geometric Pattern With Background
Source GDJ
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
A simple but elegant classic. Every collection needs one of these.
Source Christopher Burton