Greenshot is a light-weight screenshot software tool for Windows only. Unlike snagit which requires paid license, Greenshot is a free & an open source software. Some of its features include
1)Create complete or partial screenshots quickly.
2)Easily annotate, highlight or obfuscate parts of the screenshot.
3)Send the screenshot to a file, the clipboard, a printer or as e-mail attachment.
Some screenshots of greenshots :)
Altough it’s not that fancy like snagit but if you are good in programming, u can add whatever feature u like to add in this application since it’s an open source application.
It can be Download from here