A seamless pattern with a unit cell drawn as a bitmap in Paint.net and vectorized in Vector Magic.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Derived from an image that was uploaded to Pixabay by starchim01
Source Firkin
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
Tiny circle waves, almost like the ocean.
Source Sagive
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
These dots are already worn for you, so you don’t have to.
Source Matt McDaniel
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
A frame using leaves from an image that was uploaded to Pixabay by mayapujiati
Source Firkin
This one is amazing, truly original. Go use it!
Source Viahorizon
Seamless Prismatic Quadrilateral Line Art Pattern No Background
Source GDJ
A seamless pattern recreated from an image on Pixabay. It is reminiscent of parquet flooring and is formed from a square tile, which can be recovered in Inkscape by selecting the ungrouped rectangle and using shift-alt-I together.
Source Firkin
Prismatic Polka Dots 3 No Background
Source GDJ
A bit of scratched up grayness. Always good.
Source Dmitry
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
Dead simple but beautiful horizontal line pattern.
Source Fabian Schultz