I scanned a paper coffee cup. You know, in case you need it.
Source Atle Mo
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Prismatic Curved Diamond Pattern 7 No Background
Source GDJ
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a drawing in 'Analecta Eboracensia', Thomas Widdrington, 1897.
Source Firkin
This is a seamless pattern of a woody texture.The original image is here:https://pixabay.com/ja/users/ClassicallyPrinted-1302233/
Source Yamachem
Derived from an image that was uploaded to Pixabay by darkmoon1968
Source Firkin
From a drawing in 'Kingsdene', Maria Fetherstonehaugh, 1878.
Source Firkin
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
This is the remix of an Openclipart clipart called "Maze" uploaded by "any_ono_mous".Thanks.This is a seamless pattern of a maze.
Source Yamachem
Retro Circles Background 4 No Black
Source GDJ
More bright luxury. This is a bit larger than fancy deboss, and with a bit more noise.
Source Viszt Péter
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
You could get a bit dizzy from this one, but it might come in handy.
Source Dertig Media
Prismatic Hypnotic Pattern No Background
Source GDJ