Annotable - Ultimate image annotation & markup tool
Usersnap - Visual Feedback - Usersnap helps your business with its versatile feedback platform to build better, more successful products and services with the help of user feedback. Collect feedback along your product development lifecycle. Try it for free.
Airsketch - Simple screenshots + annotations for Mac 🖥️
Feedback by Pixelic - Painless design feedback and version control.
Weava - Workspace to highlight, organize & collaborate on your research articles.
Sesov - A community for anonymous design feedback