dashi by Premast - Create dashboards in a snap
Marker.io for Slack - Turn screenshots into Slack messages ✌️
Annotate by Convergely - Easily annotate images you get on Slack - just like Skitch
Glui - glui - GLUI is a GLUT-based C++ user interface library which provides controls such as buttons, checkboxes, radio buttons, and spinners to OpenGL applications. It is window-system independent, using GLUT or FreeGLUT.
Annotable - Ultimate image annotation & markup tool
Instashot - Access text from any image instantly.