What is the Cafetière (French for "Coffee machine") for?
I know that it requires loads of items to fix it; I'm just wondering what it does.
It, uh, eventually makes coffee. Coffee restores 4 AP. It does not cause addiction and no limit on the AP/day it can restore.
To make a cup of coffee, you need 1× Pharmaceutical Products, 1× Battery and 1× Rotten Log.
Just so there is a clear answer as an answer rather than in the comments of answer.
As mordi2k correctly stated in the comments, to create a "Bloody Hot Coffee" from the fixed Cafetière it requires 1 Battery, 1 Rotting Log and 1 Pharmaceutical Product.
The Bloody Hot Coffee is quite unique in that it does not count as a food, water or drug. It replenishes 4 AP per cup and can be drank an unlimited number of times within one day with no change to your status, so a player could drink 100 coffee to invest 400 AP in construction on the same day and still have no negative status effects.
Pros of coffee: unlimited use per day. If you had 100 coffee in the bank, you could spend 400AP all by yourself in one day.
Cons of coffee: trades a Pharmaceutical Product and a battery for a 4AP coffee.