InVision is a web-based prototyping tool that allows designers to create highly interactive mockups for web and mobile projects. While you can't create designs directly within InVision itself, you can upload your static page designs into the tool and then add hotspots to transform them into fully interactive mockups. Additionally, InVision has the ability to sync with your Photoshop or Sketch documents, allowing you to update your prototype in real-time within your design suite program of choice.
In terms of features, InVision has a wide array of valuable tools to facilitate your workflow including preview mode, comments, version control, and file syncing. It also offers a variety of transition animations and mobile gestures (swiping, tapping, etc.) that can help bring your design to life. One of my favourite features in InVision is its ability to create hover states for any design element. This allows your prototype to be even more representative of the final product as you can add advanced interactivity such as drop-down menus and hover states for buttons.
InVision's ability to facilitate collaboration is its greatest asset. Teammates, clients, or anyone shared on the mockup has the ability to leave location-specific comments and threads. This eliminates confusion created through back and forth email threads, and helps ensure that changes are implemented exactly where they need to be. Plus, with InVision's LiveShare feature, collaboration can happen in real-time using a screen sharing integration that includes chat, collaborator-specific mouses, and sketching capabilities.