Editor is one of the requirement while taking the long input from the user , just like there
long long comments, about us , comments, and many more editor play important role in this case , you can edit that text as per you want you can use all html tags and all to make your reply or comments or text better.
here are the some free online editor you can integrate that on you .net web application.
3. Yahoo! UI Text Editor
Download Yahoo!UI Text Editor
NicEdit is a Lightweight, Cross Platform, Inline Content Editor