In the new Minecraft 1.14 update there are several new blocks, one of which is called a composter. What does this block do? Is it just decoration, like so many other new blocks, or does it have a purpose?
There's a wiki page for this, which says:
Composters can be used to produce bone meal. To do so, the player must use any of a selection of items on the composter. The composter can also be used to recycle unneeded plant items. When an adjacent comparator is facing away from the composter, a comparator signal strength of up to 8 is emitted depending on the fullness of the block.
The full table of compostable items is available on the wiki, but in general, any plant matter or food items can be composted.
As noted by @SF. in the comments, composters can be filled and emptied via hoppers. Futhermore, composter blocks can be picked up or moved by pistons with their contents intact. This has significant implications for redstone circuitry.
Composters also serve to allow jobless villagers to choose the farmer profession if there is no other farmer in the village.