Sketch Measure - Spec tool for developers and teammates
AppReviewDesk - App Review Exchange, Free App Websites , Twitter Marketing for apps.
Zeplin - Collaboration app for UI designers & frontend developers
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.
Marketch - Marketch is a Sketch 3 plug-in for automatically generating html page that can measure and get CSS...
UserTrue - Free peer to peer app reviews. Give a review, get a review for free.