Squares #302
 Dark  CC BY-SA 3.0

Dark, square, clean and tidy. What more can you ask for?

Source Jaromír Kavan

 More Textures
Background pattern 336 (colour 2) #1720
 Green  CC 0

Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.

Source Firkin

Background pattern 235 (colour 4) #2252
 Green  CC 0

To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.

Source Firkin

The Black Mamba #769
 Dark  CC BY-SA 3.0

Super dark, crisp and detailed. And a Kill Bill reference.

Source Badhon Ebrahim

Dark Brick Pattern #1032
 Stone  CC BY-SA 3.0

A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.

Source V. Hartikainen

Brushed Aluminum 8 #1396
 Dark  CC 0

Gamedev - Metal Textures. CC0 License.

Source Davit Masia

Dark Fish [email protected] #1049
 Dark  CC BY-SA 3.0

It almost looks a bit blurry, but then again, so are fishes.

Source Petr Šulc

Retro Circles Background 4 #420
 Dark  CC 0

Retro Circles Background 4

Source GDJ

Green Background Pattern with Warped Vertical Stripes #968
 Stripes  CC BY-SA 3.0

A green background pattern with warped vertical stripes and a grunge look.

Source V. Hartikainen

Background pattern 272 (colour 3) #2055
 Red  CC 0

A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.

Source Firkin

Grass #1286
 Unknow  CC 0

Zero CC tileable dry grass texture, photographed and made by me. CC0

Source Sojan Janso

Seed #1289
 Wall  CC 0

Zero CC tileable seed texture, edited by me to be seamless from a Pixabay image. CC0

Source Sojan Janso

Prismatic Dots Background [email protected] #512
 Dark  CC 0

Prismatic Dots Background 6

Source GDJ

Pattern & Plywood #1347
 Wood  CC 0

CC0 for Free, hope you like it.

Source Yethiel

Blue & Fissure & Cube #1702
 Wall  CC 0

Background Wall, Art Abstract, Blue Well & CC0 texture.

Source Ractapopulous

Burried #831
 Dark  CC BY-SA 3.0

Have you wondered about how it feels to be buried alive? Here is the pattern for it.

Source Hendrik Lammers

Prismatic Curved Diamond Pattern 8 No Background #549
 Dark  CC 0

Prismatic Curved Diamond Pattern 8 No Background

Source GDJ

More Rough Wood 7 #1433
 Wood  CC 0

Gamedev - Wood Textures. CC0 License.

Source Davit Masia

White [email protected] #1106
 Wall  CC BY-SA 3.0

Looks like an old wall. I guess that’s it then?

Source Viahorizon

Tapestry #747
 Diamond  CC BY-SA 3.0

Tiny and subtle. What’s not to love?

Source Pixeden

Stone Wall & Yellow #1556
 Stone  CC 0

Incoming catena. Stone & well. CC0 texture.

Source Unknow

Paper [email protected] #1061
 Paper  CC BY-SA 3.0

Just what the name says, paper fibers. Always good to have.

Source Heliodor jalba

Floral divider 4 #1750
 Dark  CC 0

From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.

Source Firkin

Fabric of Squares #1095
 Light  CC BY-SA 3.0

As far as fabric patterns goes, this is quite crisp.

Source Heliodor Jalba

Beige Stripes #938
 Stripes  CC BY-SA 3.0

A repeating background of beige (or is it more vanilla yellow) textured stripes. One more background with stripes.

Source V. Hartikainen

Light Paper Fibers #835
 Paper  CC BY-SA 3.0

More in the paper realm, this time with fibers.

Source Jorge Fuentes

Background pattern 312 #1860
 Blue  CC 0

Alternative colour scheme

Source Firkin

Green Wall #1252
 Wall  CC 0

Zerro CC tillable texture of stones photographed and made by me. CC0

Source Sojan Janso

Retro Squares Background [email protected] #796
 Noise  CC 0

Retro Squares Background 8

Source GDJ

Background pattern 314 #1839
 Yellow  CC 0

The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i

Source Firkin