I refuse to believe that MonoDevelop doesn’t give you any errors, because mine goes red immediately. Also, have a look on how to use code tags properly.
Your code has several errors:
Monodevelop should be MonoBehaviour.
Gameobject should be GameObject.
onTriggerEnter should be OnTriggerEnter.
The Door variable is never assigned.
Here’s an untested revision:
public class Doorscript : MonoBehaviour
{
GameObject Door;
void Start ()
{
Door = GameObject.Find ( "Door" );
}
public void OnTriggerEnter ( Collider other )
{
if ( other.tag == "Player" )
{
Door.animation.Play( "door open" );
}
}
}