System# is a .NET library intended for the description of real-time embedded systems. It comes with a built-in simulator kernel and a code transformation engine that converts a design into synthesizable VHDL. The main focus is currently the development of FPGA designs. System# not only supports register-transfer-level (RTL) descriptions whose translation to VHDL is straightforward, but is also capable of converting clocked threads with wait statements to a synthesizable VHDL state machine. Furthermore, System# introduces synthesizable transaction-level modeling features. From a technological point of view, it uses reflection and assembly code (CIL) decompilation to reconstruct an abstract syntax tree (AST) from the system design. The AST conforms to SysDOM, a document object model for describing component-based reactive systems. An unparsing stage converts the AST to VHDL. The decompilation process can be instrumented in various ways by attribute-based programming. Furthermore, transformations of the AST itself are possible. This enables implementation of advanced features such as converting clocked threads to finite state machines.