Zeplin is another online graphics editor, supporting the collaboration between the various team members - UI/UX designers, developers and project managers in the design process.  I have the ability to integrate with Sketch, which allows designers to upload mock-ups or projects directly from Sketch and add them to Zeplin's project folders.

Annotations will be automatically added to projects (sizes, colours, margins and even CSS suggestions for some elements). Solutions of this type allow teams to co-create a project, which is the only source of truth, where each team member has immediate access to changes, corrections and comments made by another team member.