This beige background pattern resembles a concrete wall with engravings or something similar to it.
Source V. Hartikainen
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
Remixed from a drawing in 'Works. Popular edition', John Ruskin, 1886.
Source Firkin
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
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
Prismatic Hexagonalist Pattern No Background
Source GDJ
A seamless pattern of "sewn stripes" colored in light gray.
Source V. Hartikainen
You know I’m a sucker for these. Well-crafted paper pattern.
Source Mihaela Hinayon
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Zero CC tileable moss or lichen covered stone texture, edited from pixabay. CC0
Source Sojan Janso
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
Prismatic Geometric Tessellation Pattern 2 No Background
Source GDJ
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
A seamless pattern formed from a tile made from ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
A seamless texture of worn out "cardboard".
Source V. Hartikainen
Might not be super subtle, but quite original in its form.
Source Alex Smith
Tile available in Inkscape using shift-alt-i on the selected rectangle
Source Firkin