Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
The image depicts a seamless pattern of Japanese Edo pattern called "kikkou-matsu" or "亀甲松" meaning " tortoiseshell-pinetree".The real pinetree is like this: https://jp.pinterest.com/pin/500744052301065077/
Source Yamachem
Another fairly simple design drawn in Paint.net and vectorized in Inkscape.
Source Firkin
You know you love wood patterns, so here’s one more.
Source Richard Tabor
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
ZeroCC tileable stone texture, edited from pixabay, CC0
Source Sojan Janso
An interesting dark spotted pattern at an angle.
Source Hendrik Lammers
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Pattern formed from simple shapes. Black version.
Source Firkin
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
Dark pattern with some nice diagonal stitched lines crossing over.
Source Ashton
This is lovely, just the right amount of subtle noise, lines and textures.
Source Richard Tabor
Original seamless pattern with an Inkscape filter.
Source Firkin
A free tileable background colored in off-white (antique white) color.
Source V. Hartikainen
Everyone loves a diamond, right? Make your site sparkle.
Source AJ Troxell
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Alternative colour scheme for the original floral pattern.
Source Firkin