A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
Fake or not, it’s quite luxurious.
Source Factorio.us Collective
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
From a drawing in 'Studies for Stories', Jean Ingelow, 1864.
Source Firkin
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Medium gray fabric pattern with 45-degree lines going across.
Source Atle Mo
As the original image 's page size is too large for its image size, I remixed it.
Source Yamachem
Spice up your next school project with this icon background.
Source Swetha
From a drawing in 'Royal Ramsgate', James Simson, 1897.
Source Firkin
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
Detailed but still subtle and quite original. Lovely gray shades.
Source Kim Ruddock
Remixed from a drawing in 'Jezebel's Daughter', Wilkie Collins 1880
Source Firkin
Super dark, crisp and detailed. And a Kill Bill reference.
Source Badhon Ebrahim
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
Prismatic Geometric Pattern Background No Black
Source GDJ
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin