I skipped number 3, because it wasn’t all that great. Sorry.
Source Dima Shiper
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
This is the remix of an OCAL clipart called "Rain on Window" uploaded by "pagarmidna".Thanks.This is a seamless pattern of raindrops.
Source Yamachem
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
Inspired by a 1930s wallpaper pattern I saw on TV.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Zero CC bark from fur tree tileable texture, photographed and made by me. CC0
Source Sojan Janso
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
He influenced us all. “Don’t be sad because it’s over. Smile because it happened.”
Source Atle Mo
A free grid paper background pattern for using on web sites.
Source V. Hartikainen
Zero CC tileable moss or lichen covered stone texture, edited from pixabay. CC0
Source Sojan Janso
A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
Black And White Floral Pattern Background Inverse
Source GDJ
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
White fabric looking texture with some nice random wave features.
Source Hendrik Lammers