Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A repeating background for websites with a texture of black groove stripes.
Source V. Hartikainen
Looks like an old wall. I guess that’s it then?
Source Viahorizon
Old China with a modern twist, take two.
Source Adam Charlts
A background pattern with green vertical stripes. A new striped background pattern. This time a green one.
Source V. Hartikainen
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Drawn in Paint.net and vectorised in Vector Magic
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a JPG that was uploaded to Pixabay by Osckar
Source Firkin
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868
Source Firkin
I scanned a paper coffee cup. You know, in case you need it.
Source Atle Mo
Love the style on this one, very fresh. Diagonal diamond pattern. Get it?
Source INS
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The edges of all the red objects line up either vertically or horizontally, but it doesn't appear so. Made from a square tile that can be got by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Abstract Background Design
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
CC0 and seamless wellington boot pattern.
Source SliverKnight
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
A background tile of dark textile. Made this a long time ago and just now decided to publish it.
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
A seamless background pattern of dark brown wood planks.
Source V. Hartikainen
Lovely light gray floral motif with some subtle shades.
Source GraphicsWall