I've long been fascinated by Stirling engines.  Their method of
operation, where they convert essentially arbitrary heat gradients
into mechanical work, is both simple and universal.  There is
something deeply elegant about how they exploit a simple physical
property in a clever manner.  Although my daily work is very remote
from building physical engines, I still find the Stirling engine
greatly inspiring - I hope to build things that are as elegant and
simple.

Therefore, I ordered a model Stirling engine from
https://www.stirlingengine.co.uk/ and just received and assembled it.
I would probably have bought it prefabricated, but I could not find
the option on their website.  Still, while assembly was fiddly
(especially the O-rings), and I had to tune it a bit afterwards to get
it to run, it was no great difficulty.  And now I have my own tiny
Stirling engine, able to (barely) run off the heat of my hand, or
(easily) off a cup of coffee!

My hope is that I can use it as a conversation piece and run it off
available heat sources in my office, such as my laptop.  I also
considered getting a fanless passively cooled desktop computer - I've
seen cases that are essentially big blocks of aluminium - and surely
they'll provide enough heat for a Stirling engine to work...