I am looking for few nouns describing "a situation when one does too many things but achieve nothing important or useful".
You're looking for the expression spinning your wheels.
Example: They're on the grind spinning their wheels.
You can also invent your own expressions such as:
Circling around in circles (suggesting no movement or direction inspite of activity) They're pushing too hard, a door that needs pulling. Or they're pulling what needs pushing. They're pushing a brick wall. They're busy chewing the stones. They're busy chewing the rocks. They're taking one step forward and two steps back. They're trying to fleece leather out of a sheep. They're working hard counting the hairs on their own heads. They're making about turns to get there.