Unity3D editor script to run the game and extract a set number of images and save them to a file. Put this code into a file called MakeGif.cs inside a folder called "Editor"

MakeGif.cs

using System;
using UnityEditor;
using UnityEngine;
using System.Collections;

public class MakeGif : EditorWindow {


    public string folder = "ScreenshotFolder";
    public int frameRate = 25;
    public int frames;
    public int currentFrame;
    public bool recording = false;

    [MenuItem("Window/RecordGif")]
    static void MakeWindow()
    {
			var window = EditorWindow.GetWindow(typeof(MakeGif), false, "Make GIF");
		
    }

    void OnGUI()
    {

        frames = EditorGUILayout.IntField("Frames", frames);
        frameRate = EditorGUILayout.IntField("Frame Rate", frameRate);
        EditorGUILayout.LabelField("Duration", (frames / frameRate).ToString());
        folder = EditorGUILayout.TextField("Folder", folder);
        if (GUILayout.Button("Record"))
        {
            StartRecording();
        }
    }


    void StartRecording()
    {
        // Set the playback framerate (real time will not relate to game time after this).
        Time.captureFramerate = frameRate;

        // Create the folder
        System.IO.Directory.CreateDirectory(folder);
        recording = true;
        currentFrame = 0;
        EditorApplication.isPlaying = true;
    }

    void Update()
    {
        if (recording)
        {
            // Append filename to folder name (format is '0005shot.png"')
            var name = String.Format("{0}/{1:D04}shot.png", folder, Time.frameCount);

            // Capture the screenshot to the specified file.
            Application.CaptureScreenshot(name);
            currentFrame++;
            if (currentFrame > frames)
            {
                recording = false;
                EditorApplication.isPlaying = false;
            }
        }
    }
}