A frame relative to a boat moving at constant velocity is inertial: a mass dropped from the mast of the boat lands at the same place on the boat as if the boat were not moving.

Galilean invariance restricts the type of forces that are possible.

Galilean relativity implies that the laws of physics make reference to no special point, direction, time, or velocity: all of these can only be defined relatively. One cannot be “at rest”, but only at rest with respect to something.

Acceleration is not relative. If one is accelerating in an inertial frame, then they will be accelerating in all other inertial frames, with the same magnitude.