The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Here's a tile-able wood background image for use in web design.
Source V. Hartikainen
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
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
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
From a drawing in 'Hyde Park from Domesday-Book to date', John Ashton, 1896.
Source Firkin
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
This is a seamless pattern of regular hexagon which has a honeycomb structure.
Source Yamachem
Prismatic Groovy Concentric Background 2
Source GDJ
A seamlessly tile-able grunge background image.
Source V. Hartikainen
A seamless background colored in pale orange. It has a paper like texture with diagonal grid pattern.
Source V. Hartikainen
From a drawing in 'Picturesque New Guinea', J Lindt, 1887.
Source Firkin
Prismatic Curved Diamond Pattern 6 No Background
Source GDJ
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
A dark gray, sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
This is the remix of "Colorful Floral Pattern Background 3" uploaded by "GDJ". Thanks.
Source Yamachem
Just like your old suit, all striped and smooth.
Source Alex Berkowitz
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green