Good engineering-as-marketing examples?

While doing research for my IndieHackers post, I found an interesting article mentioning several engineering-as-marketing examples I haven't encountered before:

1. US Debt Clock

Basically, a "real-time" visualization of the US debt. SimilarWeb shows 1.51 million visitors per month :O This would be perfect is you were a company in the finance space, for example, trying to get some exposure.

2. Can you beat Usain Bolt Reaction Time?

A very simple piece of code embedded in NYC. Not related to any market, but I can imagine taking this concept and transferring it into many other niches (can you guess X, can you beat Y writing speed, etc.)

Have you guys seen any recent engineering-as-marketing examples?