Extractinator

It converts the worthless blocks you dig through into ore, gems and coins, one block per activation. Silt and Slush are the standard inputs and Desert Fossil is the third. Later versions widened its remit considerably: it turns glowing moss into other moss, and it turns fishing junk into low grade bait, both of which quietly solve small annoyances.

The output per block is unimpressive. The point is that the input is free and endless. Silt accumulates on its own while you are mining for something else, so the whole machine runs on material you would otherwise leave on the floor.

You cannot craft it. It turns up in Frozen Chests in the ice caves, in Gold Chests at Underground and Cavern depth, and out of Wooden Crates if you fish enough of them. The most reliable route is the underground desert, where the abandoned cabins have one sitting in the room as part of the furniture often enough to be worth a dedicated sweep. If you are hunting for one specifically, go there rather than opening every gold chest you pass.

It is the practical way to get whichever pre-Hardmode ore your world did not generate. The alternate and the native ore come out at the same rate regardless of which one your world actually contains, so a copper world can supply itself with tin without trading with another player.

It is also the only source of the Amber Mosquito, and amber more generally is the real reason to keep feeding it. Amber goes into Crate Potions, and crates pull in loot worth far more than the amber would have sold for. That loop is where most of the machine's long term value sits.

Wire it up and it pulls extractable blocks out of a chest next to it, processing one per second on a signal. Pair that with a timer and a chest you dump silt into and it runs itself while you do something else. If you are feeding it by hand instead, turn on Auto Select and it will pick the right blocks out of your inventory without you switching to them.

Clear a good chunk of inventory first, sixteen or seventeen free slots, or the results start dropping onto the floor behind you and you will lose some of them. Speed is fixed by the block itself, so building speed boosts do nothing here, which surprises people who assume it works like block placement.

It will also never produce Hardmode ore, or the high tier pre-Hardmode ores, no matter how far into the game you are. That ceiling is the entire reason the Chlorophyte Extractinator exists, and upgrading is the only way past it.

Most of the average value hides in a rare Platinum Coin roll, so a small sample always feels worse than the machine actually is. Run a thousand blocks and you either hit that jackpot or you do not, and the difference between those two outcomes is most of the session's earnings. Judge it over volume, never over a handful of blocks.

The gems are worth more as gemcorns than as coins, since a tree pays out forever. Sturdy Fossils sell for nothing at all, but they feed Scarab Bombs, and any surplus converts into Bone Throwing Knives, which do have a sale price.

Silt, almost always. It piles up on its own, it is common everywhere, and it pays better across ores, coins and gems. Desert fossil is worse on all of those except amber, and gathering it means standing around in the underground desert, which is a considerably more hostile place to be for very little extra return.

In a Skyblock world the calculation flips: Shell Piles fed through it are a sand source, which matters a great deal when there is no ground to dig.