Anything included for dealing with mouse relationshipt to 3D objects?

I've been looking through the documentation and can't seem to find anything for dealing with 3D mouse position. Any help on info for this would be great.

Here some edit code I use in C# (it has been edit here so it may syntax errors but the idea works)

RaycastHit hit;
Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
if (Input.GetMouseButtonDown(0)) {
    if (Physics.Raycast(ray , out hit , 100F)) {
    hit.collider.SendMessage("OnMouseDown" , SendMessageOptions.DontRequireReceiver);

it converts the mousePosition to ray cast from the camera position. then chacks what colliders that ray hit. So you will need colliders on your 3D object. and then sends a message to the object.

If you feed the screen position of the mouse and a z-distance into the above function, it will return a coordinate in world space.

There are numerous examples of using it you can find on the forums. Everything from click-walking for an RTS to controlling 3d cursors.