Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
An interesting dark spotted pattern at an angle.
Source Hendrik Lammers
As simple and subtle as it gets. But sometimes that’s just what you want.
Source Designova
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
A re-make of the Gradient Squares pattern.
Source Dimitar Karaytchev
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Stefan is hard at work, this time with a funky pattern of squares.
Source Stefan Aleksić
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
U.S.-based National Fire Protection Association standard fire diamond for flagging risks posed by hazardous materials. The red diamond has a number 0-4 depending on flammability. The blue diamond has a number 0-4 depending on health hazard. The yellow has a number 0-4 depending on reactivity. the white square has a special notice, e.g OX for oxidizer.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Colorful Floral Background 3 No Black
Source GDJ
Submitted as a black pattern, I made it light and a few steps more subtle.
Source Andy
It’s okay to be square! A nice light gray pattern with random squares.
Source Waseem Dahman
Inspired by the B&O Play, I had to make this pattern.
Source Atle Mo
Derived from a drawing in 'Elfrica. An historical romance of the twelfth century', Charlotte Boger, 1885
Source Firkin
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
A frame using leaves from an image that was uploaded to Pixabay by mayapujiati
Source Firkin
Fix and cc0 to get the tile this is based on.
Source SliverKnight