SharpFlash is a third-party tool (released under the GNU General Public License) allowing Flash applications to have more power on operating systems supporting the .NET Framework. It exposes (read: in the future, it will expose) an ActionScript API allowing a Flash application to have as much control over the environment as a native desktop application has. This includes things like allowing file access (both read/write), registry access, internet access, etc. The API is still under heavy development, but the code has stabilized to a pre-alpha state. Written in C#, SharpFlash takes advantage of a Flash User Interface. Additionally, SharpFlash was built with SharpFlash, demonstrating the power of the program.
Not in active development anymore.