The Rigidbody of the collider that was hit. If the collider is not attached to a rigidbody then it is null.

	// Apply a force to a clicked rigidbody object.
	
	// The force applied to an object when hit.
	var hitForce: float;
	function Update() {
		if (Input.GetMouseButtonDown(0)) {
			var hit: RaycastHit;
			var ray = Camera.main.ScreenPointToRay(Input.mousePosition);
			
			if (Physics.Raycast(ray, hit)) {
				if (hit.rigidbody != null)
					hit.rigidbody.AddForce(ray.direction * hitForce);
			}
		}
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    public float hitForce;
    void Update() {
        if (Input.GetMouseButtonDown(0)) {
            RaycastHit hit;
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            if (Physics.Raycast(ray, out hit))
                if (hit.rigidbody != null)
                    hit.rigidbody.AddForce(ray.direction * hitForce);
                
            
        }
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	public hitForce as float

	def Update() as void:
		if Input.GetMouseButtonDown(0):
			hit as RaycastHit
			ray as Ray = Camera.main.ScreenPointToRay(Input.mousePosition)
			if Physics.Raycast(ray, ):
				if hit.rigidbody != null:
					hit.rigidbody.AddForce((ray.direction * hitForce))

See Also: Physics.Raycast, Physics.Linecast, Physics.RaycastAll.