UnityCsReference is the C# reference source code for the Unity engine and editor. It provides developers transparency into how Unity's C# APIs are implemented under the hood but is strictly for reference—not for modification or redistribution without a commercial license. The terms of use do not permit you to modify or redistribute the C# code (in either source or binary form). If you want to modify Unity's source code (C# and C++), contact Unity sales for a commercial source code license....
Code Insight is a Open source, cross platform software for developers to browse, edit and understand code easily, like commercial one named SourceInsight. Based on CodeLite IDE the CodeInsight also is aligned with GPL license.