I am trying to do some wysiwyg Textbox for specific use, so I don't need usual wysiwyg, I need like buttons which will insert like [ @ or so.
I thought to add some buttons which will insert those to textbox.
Any other thoughts?
I recommend CKEditor, which is highly customizable.
The thing you try to do, is not built-in in almost any WYSIWYG editor out there (AMAIK). Thus, you should implement it on your own. But by using a third-party WYSIWYG, and customizing it (instead of creating a WYSIWYG editor entirely from scratch), you can get sure that you already have tens of other functionalities.
Also I should note that most WYSIWYG editors can become as simple as having one toolbar with basic formatting buttons (just like SO's editor).