Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
This yellow background consists of a pattern of glossy gold buttons arranged in polka dot style on a seamless texture. Here's a pale yellow background pattern. Feel free to use it for your needs!
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Kaleidoscope Prismatic Abstract No Background
Source GDJ
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
A pattern formed from a photograph of a 16th century ceramic tile.
Source Firkin
This one is amazing, truly original. Go use it!
Source Viahorizon
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Remixed from a raster on Pixabay, that was uploaded by ArtsyBee.
Source Firkin
It’s okay to be square! A nice light gray pattern with random squares.
Source Waseem Dahman
Prismatic Groovy Concentric Background 3
Source GDJ
Retro Circles Background 4 No Black
Source GDJ
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
An abstract Background pattern of purple twisty patterns.
Source TikiGiki
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Looks like an old rug or a computer chip.
Source Patutin Sergey
Bit of a strange name on this one, but still nice. Tiny gray square things.
Source Carlos Valdez