ultra simple Gravity Gun

GravityGunAccessory.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

// @kurtdekker - gravity gun attachment
//
// We presume you attached this to a new GameObject parented to a
// camera that looks where you want to fire the gravity gun.
//
// This only scans for things with a Grippable Component on them.
//
// Press Y to yoink / let go of things with the gravity gun
//
// Press T to throw it if you're carrying it
//

public class GravityGunAccessory : MonoBehaviour
{
	[Header("Where in front of you the load tries to be:")]
	public Vector3 GripAhead = new Vector3(1, 1, 4);

	[Header("We won't consider beyond this range:")]
	public float GripDistance = 10;

	// non-null means you're gripping
	Grippable current;

	// desired point in space ahead of you for carrying the object
	Vector3 center => transform.position + transform.rotation * GripAhead;

	void GripToggle( bool fling = false)
	{
		if (current)
		{
			current.rb.useGravity = true;

			if (fling)
			{
				// pure forward
				Vector3 tossDirection = transform.forward;

				// up a bit
				tossDirection.y += 0.2f;

				// scale
				tossDirection *= 30;

				// by adding, you can whip it to one side by spinning
				current.rb.velocity += tossDirection;
			}

			// let go / drop!
			current = null;
		}
		else
		{
			// TODO: feel free to implement your own object finder here.
			var grippables = FindObjectsOfType<Grippable>();

			float bestDistance = 0;
			Grippable best = null;

			foreach( var grippable in grippables)
			{
				float distance = Vector3.Distance(grippable.transform.position, center);
				if (distance < GripDistance)
				{
					if (best == null || distance < bestDistance)
					{
						best = grippable;
						bestDistance = distance;
					}
				}
			}

			if (best)
			{
				current = best;
			}
		}
	}

	void UpdateCheckGrip()
	{
		bool toggleGrip = false;
		bool fling = false;

		// check your inputs here...
		if (Input.GetKeyDown(KeyCode.Y))
		{
			toggleGrip = true;
		}
		if (Input.GetKeyDown(KeyCode.T))
		{
			toggleGrip = true;
			fling = true;
		}

		if (toggleGrip)
		{
			GripToggle(fling);
		}
	}

	void Update()
	{
		UpdateCheckGrip();
	}

	private void FixedUpdate()
	{
		if (current)
		{
			float dt = Time.deltaTime;


			// we want to hold the object here
			Vector3 target = center;

			// error term
			Vector3 delta = target - current.transform.position;

			Vector3 direction = delta.normalized;

			float distance = delta.magnitude;



			Rigidbody rb = current.rb;

			rb.useGravity = false;

			float mass = rb.mass;




			Vector3 velocity = rb.velocity;

			// tuning: velocity damping
			float velocityDamping = 10.0f;

			velocity -= velocity * velocityDamping * dt;

			rb.velocity = velocity;


			// tuning: force scaling
			float forceScale = 140.0f;



			Vector3 force = direction * distance * forceScale;



			rb.AddForce(force * mass);
		}
	}
}

Grippable.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

// tags an object as something you can grip
//
// put one of these on things you want to carry

[RequireComponent(typeof(Rigidbody))]
public class Grippable : MonoBehaviour
{
	public Rigidbody rb => GetComponent<Rigidbody>();
}