Giano is a simulation framework for the full-system simulation of arbitrary computer systems, with special emphasis on the hardware-software co-development of system software and Real-Time embedded applications. It allows the simultaneous execution of binary code on a simulated microprocessor and of Verilog code on a simulated FPGA, within a single target system capable of interacting in real-time with the outside world. The graphical user interface creates the interconnection graph of the user-provided simulation modules in PlatformXML, an XML-based platform description language. Experience with several projects reveals that the tool is effective in reducing the development and maintenance time for system software and for embedded applications. The most visible benefits are a shorter modify-compile-test cycle, better support for performance tuning and improved flaw detection. Giano is freely available in source and binary form for non-commercial use.