Which Software/Tool is used for creating Game Objects?

Hi,

I'm new to Unity. While I was watching some tutorials in the website (Unity) I came across something which says that Game Objects are created outside Unity (Not primitive types like Sphere, Cylinder etc) like Person, Hand, Yo-Yo etc.

I would like to know:

• Which Tools are used to create these Game objects outside Unity?

• Which are most compatible for Unity importing?

• Which are popular?

• Which are easy or we can call for Rapid building?

I might have sounded little different/ambiguous/OpenEnded. You can correct me as I'm a beginner here :)

Thanks in Advance, inblueswithu