Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Remixed from a drawing in 'An Index to Deering's Nottinghamia Vetus et Nova', Rupert Chicken, 1899. The unit tile can be had by selecting the rectangle in Inkscape and using shift-alt-i
Source Firkin
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
The image depicts a seamless pattern of a Japanese family crest called "chidori" in Japanese .A chidori in Japanese means a plover in English.
Source Yamachem
Background Wall, Art Abstract, Star Well & CC0 texture.
Source Ractapopulous
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Embossed lines and squares with subtle highlights.
Source Alex Parker
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
A dark pattern made out of 3×3 circles and a 1px shadow. This works well as a carbon texture or background.
Source Atle Mo
With a name this awesome, how can I go wrong?
Source Nikolay Boltachev
A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen