Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
This background pattern contains worn out colorful stripes as a texture.
Source V. Hartikainen
A free background pattern with abstract green tiles.
Source V. Hartikainen
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Non-seamless pattern drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
This background pattern has futuristic look. So, maybe it could be used on websites or blogs dedicated to video games?!
Source V. Hartikainen
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
Number five from the same submitter, makes my job easy.
Source Dima Shiper
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Here's an yet another seamless note paper texture for use as a background on websites.
Source V. Hartikainen
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
The edges of all the red objects line up either vertically or horizontally, but it doesn't appear so. Made from a square tile that can be got by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A simple but elegant classic. Every collection needs one of these.
Source Christopher Burton
Embossed lines and squares with subtle highlights.
Source Alex Parker
An abstract texture of water. It's not perfect, but will do. You may download if you like it.
Source V. Hartikainen
Basket Fibers, Basket Texture, Braid Background style CC0 texture.
Source 1A-Photoshop
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Groovy Concentric Background 5
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin