This is AvalonEdit 4.3.1.9430. Code Project article: http://www.codeproject.com/KB/edit/AvalonEdit.aspx AvalonEdit website: http://www.avalonedit.net/ SharpDevelop website: http://www.icsharpcode.net/OpenSource/SD/ Copyright Daniel Grunwald, 2008-2013 ICSharpCode.AvalonEdit is licensed under the GNU LGPL. See license.txt for details. The AvalonEdit.Sample application is licensed under the MIT/X11 license. See the file headers of AvalonEdit.Sample\*.cs for details.