CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Paper model of a tetrahedron. Modelo de papel de um tetraedro.
Source laobc
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Nice little grid. Would work great as a base on top of some other patterns.
Source Arno Gregorian
Light gray grunge wall with a nice texture overlay.
Source Adam Anlauf
CC0 remixed from a drawing. Walter Crane, 1914, Firkin.
Source SliverKnight
You could get a bit dizzy from this one, but it might come in handy.
Source Dertig Media
From an image on opengameart.org shared by rubberduck.
Source Firkin
If you don’t like cream and pixels, you’re in the wrong place.
Source Mizanur Rahman
One more brick pattern. A bit more depth to this one.
Source Benjamin Ward
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
This is a seamless pattern which is derived from a flower petal image.
Source Yamachem
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Background formed from the original with an emboss effect
Source GDJ