Produced using the clouds, flames and glass blocks plug-ins in Paint.net and the resulting .PNG vectorised with Vector Magic.
Source Firkin
A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Dark Tile-able Grunge Texture. I think this texture can be classified as grunge. It's free and seamless, as always.
Source V. Hartikainen
Prismatic Geometric Pattern Background No Black
Source GDJ
Hexagonal dark 3D pattern. What more can you ask for?
Source Norbert Levajsics
From a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
The image depicts a seamless pattern of Japanese Edo pattern called "kikkou-matsu" or "亀甲松" meaning " tortoiseshell-pinetree".The real pinetree is like this: https://jp.pinterest.com/pin/500744052301065077/
Source Yamachem
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
Paper pattern with small dust particles and 45-degree strokes.
Source Atle Mo
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
A bit strange this one, but nice at the same time.
Source Diogo Silva
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Zero CC tileable wood texture, made by me procedurally in Neo Texture Edit.
Source Sojan Janso
Prismatic Groovy Concentric Background 2
Source GDJ
Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
Colour version of the original pattern inspired by the front cover of 'Old and New Paris', Henry Edwards, 1894.
Source Firkin
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Seamless Dark Grunge Texture. Here's a new grunge texture for use as a background.
Source V. Hartikainen
From a drawing in 'Worsborough; its historical associations and rural attractions', Joseph Wilkinson, 1879.
Source Firkin
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Prismatic Groovy Concentric Background 3
Source GDJ
More carbon fiber for your collections. This time in white or semi-dark gray.
Source Badhon Ebrahim
Seamless tile drawn in Paint.net and vectorised in Vector Magic.
Source Firkin