Side-by-side comparison of Grunt and Gulp configuration. Only significant difference is that `gulp-concat` doesn't generate source maps like `grunt-concat-sourcemaps`.

grunt.js

/* jshint node: true */

module.exports = function(grunt) {
  require('load-grunt-tasks')(grunt);

  grunt.initConfig({
    transpile: {
      main: {
        type: 'amd',
        moduleName: function(path) {
          return grunt.file.readJSON('package.json').name + path;
        },
        files: [{
          expand: true,
          cwd: 'src/',
          src: '**/*.js',
          dest: 'tmp/transpiled/'
        }]
      }
    },
    concat_sourcemap: {
      main: {
        src: 'tmp/transpiled/**/*.js',
        dest: 'tmp/game.js',
        options: {
          sourceRoot: ".."
        }
      }
    },
    watch: {
      main: {
        files: ["src/**/*.js"],
        tasks: ["default"]
      }
    },
    connect: {
      server: {
        options: {
          port: process.env.PORT || 8000,
          hostname: '0.0.0.0',
          base: '.'
        }
      }
    }
  });

  grunt.registerTask("default", ["transpile", "concat_sourcemap"]);
  grunt.registerTask("dev", ["default", "connect", "watch"]);
};

gulp.js

/* jshint node: true */
var gulp = require('gulp');

var g = require('gulp-load-plugins')();

var scriptFiles = './src/**/*.js';

gulp.task('buildJs', function() {
  gulp.src('./src/**/*.js')
    .pipe(g.es6ModuleTranspiler({
      type: 'amd',
      moduleName: function(path) {
        return require('./package.json').name + '/' + path;
      }
    }))
    .pipe(g.concat('game.js'))
    .pipe(gulp.dest('./tmp'));
});

gulp.task('connect', g.connect.server({
  port: process.env.PORT || 8000,
  hostname: '0.0.0.0',
  root: __dirname
}));

gulp.task('watch', function() {
  gulp.watch(scriptFiles, ['buildJs']);
});

gulp.task('default', ['buildJs']);
gulp.task('dev', ['buildJs', 'connect', 'watch']);