From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Seamless tile drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
Remixed from an image that was uploaded to Pixabay by CatherineClennan
Source Firkin
The tile this is based on was adapted from an image that was uploaded to Pixabay by frolicsomepl. It can be had in Inkscape by selecting the rectangle and using shift+alt+i
Source Firkin
Prismatic Floral Background No Black
Source GDJ
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
This background pattern contains a seamless texture of bark. It's not very realistic, but I think it looks quite nice.
Source V. Hartikainen
A seamlessly tileable pink background texture.
Source V. Hartikainen
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Adapted from an image that was uploaded to Pixabay by Anerma.
Source Firkin
Prismatic Triangular Seamless Pattern III With Background
Source GDJ
Retro Circles Background 5 No Black
Source GDJ
Zero CC tileable seed texture, edited by me to be seamless from a Pixabay image. CC0
Source Sojan Janso
Abstract Tiled Background Extended 10
Source GDJ