“The mirrors are angled so that just before sunset on our 8th anniversary, it reflects the light from the setting sun onto the ground to spell out “MARRY ME?””
A grid of one-inch mirror tiles on a printed hex base, each one angled by a Python script to land a single pixel of sunlight. The whole thing only works at one place and one moment of one day. He open-sourced the code anyway. Most proposals cost a ring and a dinner. This one cost a ray tracer.