I love this simple freeware tool.

it takes an image (heightmap)
and turns it into a 3d .obj mesh!

so useful and fast for 1 minute lowpoly experiments, trims, details, greebles, etc! #gamedev

http://www.chestnutpens.co.uk/misc/heightmap.html

♥ (no installers, ads, or logins, just a 3MB portable .exe)