Number five from the same submitter, makes my job easy.
Source Dima Shiper
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
Wild Oliva or Oliva Wilde? Darker than the others, sort of a medium dark pattern.
Source Badhon Ebrahim
Same classic 45-degree pattern, dark version.
Source Luke McDonald
Background formed from the iconic plastic construction bricks that gave me endless hours of fun when I was a lad.
Source Firkin
Actually remixed from a pattern on Pixabay. But then noticed a very similar one on Openclipart.org uploaded by btj51q2.
Source Firkin
Prismatic Hexagonalism Pattern No Background
Source GDJ
A background tile of dark textile. Made this a long time ago and just now decided to publish it.
Source V. Hartikainen
A very dark asfalt pattern based off of a photo taken with my iPhone.
Source Atle Mo
Zero CC tileable hard cover red book, scanned and made by me. CC0
Source Sojan Janso
Like the name suggests, this background image consists of a pattern of dark bricks. It may be an option for you, if you are looking for something that looks like a brick wall for use as a background on web pages. It's not a masterpiece, but looks pretty nice when is tiled.
Source V. Hartikainen
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A free seamless background texture of "timber wall" (colored in dark brown).
Source V. Hartikainen
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
Prismatic Abstract Background Design No Black
Source GDJ
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Did anyone say The Hoff? This pattern is in no way related to Baywatch.
Source Josh Green
Kaleidoscope Prismatic Abstract No Background
Source GDJ
Colour version of the original pattern inspired by the front cover of 'Old and New Paris', Henry Edwards, 1894.
Source Firkin
Gold Triangular Seamless Pattern No Background
Source GDJ