Greenshot - Greenshot is a free and open source screenshot tool that allows annotation and highlighting using the built-in image editor.
ScreenTray - A better way to capture, annotate and share screenshots
Snagit - Screen Capture Software for Windows and Mac
Annotate by Convergely - Easily annotate images you get on Slack - just like Skitch
MWSnap - MWSnap is basically a free to use Windows snapping tools that are used for snapping any part of the screen that is currently displaying on the front of all opened programs and windows.
Weava - Workspace to highlight, organize & collaborate on your research articles.