Board.cs

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

public class Board : MonoBehaviour {

	public GameObject keyPrefab;
	public Display display;

	private static string[] keyboardStr = {
		"1,!,1, 2,\",1, 3,#,1, 4,$,1, 5,%,1, 6,&,1, 7,\',1, 8,(,1, 9,),1, 0,0,1",
		"q,Q,1, w,W,1,  e,E,1, r,R,1, t,T,1, y,Y,1, u,U,1,  i,I,1, o,O,1, p,P,1",
		"a,A,1, s,S,1,  d,D,1, f,F,1, g,G,1, h,H,1, j,J,1,  k,K,1, l,L,1",
		"sft,SFT,1.5, z,Z,1, x,X,1, c,C,1, v,V,1, b,B,1, n,N,1, m,M,1, BS,BS,1.5" ,
		"space,space,4",
	};

	List<GameObject[]> keyList = null;

	// Use this for initialization
	void Start () {

		Quaternion r = transform.rotation;
		transform.rotation = Quaternion.Euler (0, 0, 0);

		float maxLineWidth = 0;
		float[] lineWidth = new float[ keyboardStr.Length ];

		keyList = new List<GameObject[]> ();

		int lines = keyboardStr.Length;

		for (int i = 0; i < lines; i++) {
			string[] keyInfoArray = keyboardStr [i].Split (',');
			lineWidth [i] = 0.2f;
			int arraySize = keyInfoArray.Length / 3;
			GameObject[] keys = new GameObject[arraySize];
			for (int j = 0; j < arraySize; j++) {
				string a = keyInfoArray [j * 3 + 0].Trim();
				string A = keyInfoArray [j * 3 + 1].Trim();
				float kw = float.Parse (keyInfoArray [j * 3 + 2]);
				keys[j] = GameObject.Instantiate (keyPrefab);
				keys [j].transform.parent = transform;
				keys [j].name = "key-" + a;
				Key key = keys [j].GetComponent<Key> ();
				key.Init (this, a, A, kw);

				if (j > 0)
					lineWidth[i] += 0.1f;
				lineWidth [i] += kw;
			}

			keyList.Add (keys);
			if (lineWidth [i] > maxLineWidth) {
				maxLineWidth = lineWidth [i];
			}
		}

		float keyHeight = 1 / (lines * 1.1f + 0.1f); 
		float keyWidth = 1 / maxLineWidth;

		float y = 0.5f - 0.6f * keyHeight;
		for (int i = 0; i < lines; i++) {
			GameObject[] keys = keyList [i];
			float x = -0.5f + 0.1f * keyWidth + (1-lineWidth[i]/maxLineWidth)/2;
			for (int j = 0; j < keys.Length; j++) {
				Key key = keys [j].GetComponent<Key> ();
				x += (key.width / 2)* keyWidth;
				keys [j].transform.localPosition = new Vector3 (x, 0.1f, y);
				keys [j].transform.localScale = new Vector3 (keyWidth*key.width, 1, keyHeight);
				x += (key.width / 2 + 0.1f)* keyWidth;
			}
			y -= 1.1f * keyHeight;
		}

		transform.rotation = r;
	}
	
	// Update is called once per frame
	void Update () {
	
	}

	public void keyPressed(Key key) {
		if (display != null) {
			if (key.keyString == "sft") {
				foreach (GameObject[] keys in keyList) {
					for (int i = 0; i < keys.Length; i++) {
						Key k = keys [i].GetComponent<Key> ();
						k.shift = !k.shift;
					}
				}
			} else if (key.keyString == "BS") {
				display.Delete ();
			} else if (key.keyString == "space") {
				display.Append (" ");
			} else {
				display.Append (key.shift ? key.keyStringShift : key.keyString);
			}
		}
	}
}

Display.cs

using UnityEngine;
using System.Collections;

public class Display : MonoBehaviour {

	private string _text;
	public string text {
		get {
			return _text;
		}
		set {
			_text = value;
			if (textMesh != null) {
				textMesh.text = _text;
			}
		}
	}

	public TextMesh textMesh;

	// Use this for initialization
	void Start () {
	
		if (textMesh != null) {
			if (text != null && text != "") {
				textMesh.text = text;
			} else {
				text = textMesh.text;
			}
		}
	}
	
	// Update is called once per frame
	void Update () {
	
	}

	public void Append(string a) {
		text += a;
	}

	public void Delete() {
		text = text.Substring (0, text.Length - 1);
	}
}

Key.cs

using UnityEngine;
using System.Collections;

public class Key : MonoBehaviour {

	public Board board;
	public TextMesh textMesh;

	public string keyString;
	public string keyStringShift;
	public float width;

	private Vector3 origPos;

	private bool isShift;
	public bool shift {
		get {
			return isShift;
		}
		set {
			isShift = value;
			if (textMesh != null) {
				textMesh.text = isShift ? keyStringShift : keyString;
			}
		}
	}

	private float pushedTime;


	public void Init(Board board, string a, string A, float width) {
		this.board = board;
		keyString = a;
		keyStringShift = A;
		this.width = width;
		shift = false;
		if (textMesh != null) {
			Vector3 orig = textMesh.transform.localScale;
			textMesh.transform.localScale = new Vector3 (orig.x * (1 / width), orig.y, orig.z);
		}
	}

	// Use this for initialization
	void Start () {
		pushedTime = 0;
	}
	
	// Update is called once per frame
	void Update () {
	
	}

	public void Push() {
		if (pushedTime == 0f) {
			pushedTime = Time.time;
			origPos = transform.localPosition;
			Vector3 newPos = new Vector3 (origPos.x, origPos.y-0.1f, origPos.z);
			iTween.MoveTo(gameObject, iTween.Hash("position", newPos, "islocal", true, "oncomplete", "PushAnimCompleted", "time", 0.25f));

			if (board != null) {
				board.keyPressed (this);
			}
		}
	}

	public void PushAnimCompleted() {
		iTween.MoveTo(gameObject, iTween.Hash("position", origPos, "islocal", true, "oncomplete", "ReturnAnimCompleted", "time", 0.25f));
	}

	public void ReturnAnimCompleted() {
		pushedTime = 0;
	}
}