Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Tiny little flowers growing on your screen. Nice, huh?
Source Themes Tube
Number 2 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Pattern Background, Texture, Photoshop Structure style CC0 texture.
Source Darkmoon1968
A new take on the black linen pattern. Softer this time.
Source Atle Mo
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
A new take on the black linen pattern. Softer this time.
Source Atle Mo
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
Just what the name says, paper fibers. Always good to have.
Source Heliodor jalba
Pixel by pixel, sharp and clean. Very light pattern with clear lines.
Source M.Ashok
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
This one is so simple, yet so good. And you know it. Has to be in the collection.
Source Gluszczenko
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
A seamless tessellation pattern. To get the tile this is formed from, select the pattern in Inkscape and use shift+alt+i.
Source Firkin
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
I skipped number 3, because it wasn’t all that great. Sorry.
Source Dima Shiper
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
Prismatic Geometric Pattern Background
Source GDJ
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