ScreenTray - A better way to capture, annotate and share screenshots
Instashot - Access text from any image instantly.
Greenshot - Greenshot is a free and open source screenshot tool that allows annotation and highlighting using the built-in image editor.
Clerk Chat - SMS for Slack
ShareX - ShareX is a free and open source program that lets you capture or record any area of your screen...
Annotate by Convergely - Easily annotate images you get on Slack - just like Skitch