Under "bits" we sum up all small interchangeable tool accessories.
Screwdriver bits are often magnetic and have a hexagonal shaft that fits into the appropriate bit screwdriver. The common 1/4" variety can also be driven by cordless drills or a socket wrench (adapter available).
Router bits are special end mills that are only suitable for wood, often produce defined profiles and may be equipped with bearings as guides.
A basic set of Router bits is available at the CoMakingSpace:
Rotary Tool Bits
Best used at high speeds, these bits are often quite small and may exhibit exotic burr or sander shapes. Small grinding discs or polishers are also available.