Animal Farm mod.
No new items, mobs, interfaces etc. You automate things by taming mobs and making them work for you.
To tame a mob, you have to reduce it to low health and then click with his respective favorite item (cactus for creeper, graaains for zombie, Endstone for Enderman etc)
To tell them what to do you use fences (to show work area), items in frames (to filter by item), texts on signs and books, etc.
Spiders grow crops.
Zombies carry things.
Pigs breed ans slaughter animals.
Creepers turn ores into ingots (possibly doubling them).
Endermen mine and build structures.
Skeletons kill aggressive mobs.
Witches brew potions and craft things.