Just Enough Items.
It was made as a substitute for the old NEI when Chickenbones' disappearance meant that his mods did not get updated past Minecraft 1.8(.0)
And now it is pretty much the permanent substitute of NEI, since the new maintainers of NEI decided to strip NEI of pretty much all functionality that JEI already contained.
So I got JEI working but I had to totally remove NEI from the mods folder for it to work. What is the purpose of NEI existing still?