Answer:
I think this gentleman misspelled 'pony'. Cos' they're well cute.
In my opinion, the electrical grid. It makes possible a wide range of other creature comforts, including automatic central heat/air conditioning, easy food storage and preparation, and indoor plumbing - even in remote areas.
Internal plumbing systems have helped prevent millions of deaths caused by dissentry and diahrhoea, and have contributed greatly to the overall health and wellbeing of the human race.
I think the bike is an example of a perfect invention, the design of which hasn't really needed to be changed for 100 years or more. Bikes enable transportation of people and goods, over a huge variety of terrain, where other vehicles would not be able to go. They don't create any waste or require any extra parts or fuel once assembled. They can improve fitness and health, and reduce pollution and congestion in major cities. In rural areas they can provide a very low cost way for people to get around.