Mirrored Squares #123
 Dark  CC BY-SA 3.0

Did some testing with Repper Pro tonight, and this gray mid-tone pattern came out.

Source Atle Mo

 More Textures
Background pattern 306 (colour 4) #1877
 Colorful  CC 0

Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.

Source Firkin

Background pattern 231 #2301
 Dark  CC 0

A seamless pattern based on a tile that can be achieved by selecting the rectangle in Inkscape and using shift+alt+i.

Source Firkin

Prismatic Isometric Cube Extra Pattern No Background #405
 Light  CC 0

Prismatic Isometric Cube Extra Pattern No Background

Source GDJ

Prismatic Geometric Pattern Variation 2 With Background #471
 Noise  CC 0

Prismatic Geometric Pattern Variation 2 With Background

Source GDJ

Paper model of a tetrahedron #139
 Unknow  CC 0

Paper model of a tetrahedron. Modelo de papel de um tetraedro.

Source laobc