If you need a Syntax Highlighting Code/Text editor widget for your C# projects you might come across ScintillaNET. I commend the guys involved with that project for putting in the effort but after reviewing their output I decided that embedding Scintilla wasn’t a great solution for my application.
Instead I’ve integrated the ICSharpCode.TextEditor widget from SharpDevelop 2.2. SharpDevelop is licensed under the LGPL and as the TextEditor widget is a DLL this is compatible with both Open Source and proprietary software.
The SharpDevelop TextEditor widget is fantastic and supports an absolute cavalcade of awesome features such as syntax highlighting, text folding, code completion, and more. It is also amazingly easy to use in a C# or VB.Net application. I highly recommend using it if you have the need.
The only thing I could ask for is for it to be distributed as an independent control outside of the greater SharpDevelop project.