Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
A bit strange this one, but nice at the same time.
Source Diogo Silva
Prismatic Triangular Background Design Mark II 5
Source GDJ
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.
Source Ivan Ginev
Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
More in the paper realm, this time with fibers.
Source Jorge Fuentes
An alternative colour scheme to the original seamless pattern.
Source Firkin
Used in small doses, this could be a nice subtle pattern. Used on a large surface, it’s dirty!
Source Paul Reulat
A seamless pattern formed from a tile made from page ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'A Rolling Stone. A tale of wrongs and revenge', John Hartley, 1878.
Source Firkin
Prismatic Snowflakes Pattern 3 No Background
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
Retro Circles Background 7 No Black
Source GDJ
First pattern tailor-made for Retina, with many more to come. All the old ones are upscaled, in case you want to re-download.
Source Atle Mo
A seamless pattern formed from a square tile based on a jpg on Pixabay. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin
No idea what Nistri means, but it’s a crisp little pattern nonetheless.
Source Markus Reiter
Dark Tile-able Grunge Texture. I think this texture can be classified as grunge. It's free and seamless, as always.
Source V. Hartikainen
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
The image a seamless pattern derived from a weed which I can't identify.The original weed image is from here:https://jp.pinterest.com/pin/500744052301423641/
Source Yamachem
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin