InVision is a high-level prototyping tool where you prototype your designs to get a better understanding of the interactions within the app along with showing off the flows of your app. You can share these prototypes with clients and developers so that they get a better understanding of how the app works. Using InVision is very easy, the simple to use Interface lets you drag and drop all your design files like PSD, JPEGs or PNGs. You can link all the screens to create a flow for the application using hotspots and finally share the link with clients.
Zeplin is a plugin for the Sketch App and Photoshop which allows you to generate the visual assets and specifications of your design which you can then share with your developers. Using Zeplin, designers can easily and automatically generate specs, style guides and resources and share it with their developers.