The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A version without colours blended together to give a different look.
Source Firkin
Retro Circles Background 5 No Black
Source GDJ
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
From an image on opengameart.org shared by rubberduck.
Source Firkin
It’s a hole, in a pattern. On your website. Dig it!
Source Josh Green
A heavy dark gray base, some subtle noise and a 45-degree grid makes this look like a pattern with a tactile feel to it.
Source Atle Mo
Actually remixed from a pattern on Pixabay. But then noticed a very similar one on Openclipart.org uploaded by btj51q2.
Source Firkin
Remixed from a drawing in 'Hungary. A guide book. By several authors', 1890.
Source Firkin
CC0 remixed from a drawing. Walter Crane, 1914, Firkin.
Source SliverKnight
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
All good things come in threes, so I give you the third in my little concrete wall series.
Source Atle Mo
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Background Wall, Art Abstract, Watercolor Vintage style CC0 texture.
Source Ractapopulous
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Colorful Floral Background 3 No Black
Source GDJ
Derived from an image that was uploaded to Pixabay by darkmoon1968
Source Firkin
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
Inspired by a design found in 'Konstantinápolyi emlékeim', Miklos Chriszto, 1893.
Source Firkin
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
Prismatic Basic Pattern 2 No Background
Source GDJ