From a drawing in 'Two Women in the Klondike', Mary Hitchcock, 1899.
Source Firkin
Geometric lines are always hot, and this pattern is no exception.
Source Listvetra
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Remixed from a drawing that was uploaded to Pixabay by DavidZydd
Source Firkin
Could be paper, could be a Polaroid frame – up to you!
Source Chaos
Prismatic Groovy Concentric Background
Source GDJ
This one is amazing, truly original. Go use it!
Source Viahorizon
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Prismatic Abstract Geometric Background 5
Source GDJ
After 1 comes 2, same but different. You get the idea.
Source Hendrik Lammers
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Prismatic Geometric Tessellation Pattern 2 No Background
Source GDJ
Has nothing to do with toast, but it’s nice and subtle.
Source Pippin Lee
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ
A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
A seamless background tile of aged paper with shabby look.
Source V. Hartikainen
A rusty grunge background for websites. Feel free to use it in your site's theme.
Source V. Hartikainen
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
A new one called white wall, not by me this time.
Source Yuji Honzawa
Bigger is better, right? So here you have some large carbon fiber.
Source Factorio.us Collective