Jitbit's ASP.NET Forum Software is available in the form of source codes. The developer license comes with all the "codebehind" files and "business-logic" sources.
ASP.NET forum source codes are in plain C# programming language. No third-party libraries or unmanaged code involved. All the source code is included with the package and comes in a form of Visual Studio Solution file.
Buying the source codes allows modifying them in any way you wish. You're just not allowed to resell or redistribute your derivative works under your own brand (unless you purchase the OEM license). But modifying the sources for your own needs is more than welcome.