[farseer]

Mine are energy related:

1. The Steam engine and later ICE engines that started and sustained the industrial revolution and the modern world.

2. Electricity (generation, control), this led to the telegraph (our first internet), radio, and of-course electrical switching components that form basis of modern semiconductors.

[btschaegg]

If I can add to that: A precursor to both of those would be the precision lathe, from which eventually two of the most crucial prerequisites for the industrialization stem: The ability to a) produce machine parts with a high degree of precision catered for their purpose and/or context, and b) the ability to develop widely established norms these parts can adhere to (or, if you will, by which they could be judged).

The steam engine wouldn't have had its impact without the possibility for e.g. precision engineered pistons, and any industrialization would have been severely impaired without the possibilities that the distributed production of exchangeable parts (even as simple as screws, nuts and bolts) to established norms came with.