Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
This could be a hippy vintage wallpaper.
Source Tileable Patterns
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Psychedelic Geometric Background No Black
Source GDJ
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
Here's a tile-able wood background image for use in web design.
Source V. Hartikainen
The classic notebook paper with horizontal stripes.
Source Are Sundnes
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
The base gradient edited so now more details are rendered.
Source Lazur URH
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
Fix side and a seamless pattern formed from circles.
Source SliverKnight
Some dark 45 degree angles creating a nice pattern. Huge.
Source Dark Sharp Edges
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin