A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A frame using leaves from an image that was uploaded to Pixabay by mayapujiati
Source Firkin
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ
Hey, you never know when you’ll need a bird pattern, right?
Source Pete Fecteau
A seamless pattern formed from a tile made from ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
White circles connecting on a light gray background.
Source Mark Collins
Remixed from a drawing in 'Очерки Русской Исторіи въ памятникахъ быта', Petr Polevoi, 1879.
Source Firkin
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay
This is a seamless pattern of a woody texture.The original image is here:https://pixabay.com/ja/users/ClassicallyPrinted-1302233/
Source Yamachem
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
Dark, lines, noise, tactile. You get the drift.
Source Anatoli Nicolae
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
Classic vertical lines, in all its subtlety.
Source Cody L
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
If you’re sick of the fancy 3D, grunge and noisy patterns, take a look at this flat 2D brick wall.
Source Listvetra
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin