Old Mathematics@2X #44
 Stripes  CC BY-SA 3.0

This one takes you back to math class. Classic mathematic board underlay.

Source Josh Green

 More Textures
Pinstripe #35
 Light  CC BY-SA 3.0

Light gray pattern with a thin pinstripe.

Source Brandon

Concrete Wall 2@2X #80
 Wall  CC BY-SA 3.0

A light gray wall or floor (you decide) of concrete.

Source Atle Mo

Prismatic Polka Dots 3 No Background #528
 Noise  CC 0

Prismatic Polka Dots 3 No Background

Source GDJ

Prismatic Curved Diamond Pattern 2 No Background@2X #539
 Diamond  CC 0

Prismatic Curved Diamond Pattern 2 No Background

Source GDJ

Background pattern 258 #2135
 Dark  CC 0

Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.

Source Firkin

Prismatic Groovy Concentric Background 2 No Black@2X #456
 Noise  CC 0

Prismatic Groovy Concentric Background 2 No Black

Source GDJ

Tessellation 14 variant 1 #2530
 Grid  CC 0

A seamless pattern formed from a modified version of rwwgub's tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.

Source Firkin

Retro Squares Background 2@2X #417
 Noise  CC 0

Retro Squares Background 2

Source GDJ

Background pattern 225 (colour 6) #2322
 Brown  CC 0

Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.

Source Firkin

Paper 3@2X #32
 Paper  CC BY-SA 3.0

Light gray paper pattern with small traces of fiber and some dust.

Source Atle Mo

Geometric pattern #2004
 Grid  CC 0

A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i

Source Firkin