CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
The image depicts meshed silhouettes of various things.The original image is an OCAL clipart called "Enter FOSSASIA 2016 #IoT T-shirt Design Contest" uploaded by "openclipart".Thanks.
Source Yamachem
Derived from elements found in a floral ornament drawing on Pixabay.
Source Firkin
Same classic 45-degree pattern, dark version.
Source Luke McDonald
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
This is sort of fresh, but still feels a bit old school.
Source Martuchox
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
One more sharp little tile for you. Subtle circles this time.
Source Blunia
Almost like little fish shells, or dragon skin.
Source Graphiste
Adapted from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
The image depicts polka dot seamless pattern.
Source Yamachem
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
A seamless web background with texture of aged grid paper.
Source V. Hartikainen
Looks like an old rug or a computer chip.
Source Patutin Sergey
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
Retro Circles Background 5 No Black
Source GDJ
I guess this is inspired by the city of Ravenna in Italy and its stone walls.
Source Sentel
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein