Stephen Altamirano and Harry Sadler's Umbragram is a puzzler that requires you to build a 3D model that casts a shadow that matches the silhouettes on either side of it.

You left-mouse click to place blocks, rotate the play area with left arrow/A key or right arrow/D key, and z undoes one move. A few stages in, you'll have to rotate several times to figure out how to place the blocks appropriately, providing a pleasant perceptual challenge.

Umbragram is a freeware puzzler for Windows and Mac that was written in Lua, using the free Love2D framework. I didn't see a way to save, so if this game looks interesting to you, be prepared to invest some time!

[source: TIGSource devlog magazine]