AppReviewDesk - App Review Exchange, Free App Websites , Twitter Marketing for apps.
Smartmockups - Create stunning product mockups, easily and online.
Review Lancer - Reviewlancer also provide a platform for Developers or Marketers to free exchange app reviews and ratings. Now market your app for zero budget.
AppLaunchpad - Create free beautiful screenshots for App store/Google play
UserTrue - Free peer to peer app reviews. Give a review, get a review for free.
Placeit - Generate realistic product shots in seconds