A seamless background of warped stripes on paper.
Source V. Hartikainen
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
From a drawing in 'Danmarks Riges Historie af J. Steenstrup, Kr. Erslev, A. Heise, V. Mollerup, J. A. Fridericia, E. Holm, A. D. Jørgensen', 1897.
Source Firkin
A set of paper filters. The base texture is generated the same way, only the compositing mode is varied.
Source Lazur URH
Sweet and subtle white plaster with hints of noise and grunge.
Source Phil Maurer
Seamless Prismatic Geometric Pattern With Background
Source GDJ
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
Black And White Floral Pattern Background Inverse
Source GDJ
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857
Source Firkin
Inspired by a design found in 'Konstantinápolyi emlékeim', Miklos Chriszto, 1893.
Source Firkin
By popular request, an outline version of the pentagon pattern.
Source Atle Mo
Utilising a bird from s-light and some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Zero CC bark from fur tree tileable texture, photographed and made by me. CC0
Source Sojan Janso
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Oh yes, it happened! A pattern in full color.
Source Atle Mo
This light background pattern has a texture of "frozen" surface with diagonal stripes. Here's an yet another addition to the collection of free website backgrounds.
Source V. Hartikainen
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
Remixed from a PNG that was uploaded to Pixabay by k_jprather
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ