1. a power supply - the most common are either a mainspring (mechanical) or a battery (electronic). You can play around with how you power both - mainsprings can be manually wound, self-winding through wear (a weight moves around and winds it). Outside of the wristwatch world there are other cool winding mechanisms, such as air pressure variation. With electronic ones the basic options are replaceable, self-charging through motion, self charging through sunlight, or directly rechargeable.
2. an oscillator - the most common are a quartz crystal (electronic) or a hairspring (mechanical), but there are some other oddball ones out there. Most of the innovation here is around making the performance temperature/humidity/position agnostic, but at the high end there is a lot of play with new materials and architectures.
3. an interface - the most common is the 12 hour clock face (mechanical) or the LED digital interface (electronic). Although both can immediate the other, for example a jump-hour mechanical interface can resemble a digital clock. Here I think the fun stuff is mostly on the mechanical side - there are many, many cool "complications" which through some series of gears can allow a watch to also keep track of the day, month, moon cycle, day of week, year, leap year, tide (set locally), an alarm, or a a chime every hour. Of course you can do all of that digitally but I guess it feels less special
What's really fun, which this article is focused on, are the combo watches. My three favorite lineages:
Seiko Spring Drive watches are in the article - mechanical power supply, electronic oscillator.
Bulova Acutron - electronic power supply, mechanical oscillator. This one is pretty special as the oscillator was a magnet-driven tuning fork. It was far ahead of its time in terms of accuracy, but of course a dead end as far as practicality goes. It has a cool but annoying property of audibly humming.
Citizen Cosmotron - an electric power supply, mechanical oscillator. This is a more tradition hybrid, where the oscillator is a balance spring. This lineage has some neat engineering for setting the date+day of week - the orientation of the watch actually controls which complication you are working with, using the same button. Also this has a time-sync feature where you can snap the second hand to 12:00 with a press of the button and the watch pauses until you let go of said button.
New mechanical oscillators: https://www.hodinkee.com/articles/the-silicon-powered-speed-... https://www.hodinkee.com/articles/zenith-defy-lab-oscillator...