Imagesource: https://fjkraan.home.xs4all.nl/

Caution: Controversy ahead! Which was the real first programmable computer?

Wikipedia says: With his development of the Z3 in 1941, [Konrad] Zuse built the first functional, fully automatic, program-controlled and freely programmable computer operating in binary floating-point arithmetic, and thus the world's first functional computer.

Until 1998 it was believed, that the Z3 was not Turing-complete, and therefore its architectural concept was not pursued further. Later it turned out that Turing-completeness was actually given, but even without that, the machine was the first functional universal computer in the world. 

The mentioned Z3 was based on electromechanical relays. The initial predecessor machine - Z1 - was purely mechanical. And here it gets interesting. Because F.J. Kraan took a closer look at the functional principles of the machine, and was especially interested in how Zuse implemented the basic logic operators like NOT, AND, OR, XOR and XNOR from 1935 to 1938 just using mechanics.

His post additionally goes into detail about a memory element and a 3-to-8 decoder. Exciting to see how you can build a working computer without electrical fields and electrons pacing around in semiconductors.