Port/write a simple bootloader download app

I have a .net C# app I need to port to MAC. [login to view URL] I has to send a stream of 'a' characters to the devise when you press "open" for 10 seconds to make the connection. A receipt is send to the program from the device when a proper connection is established. Afterwards the program has to upload a .txt file through a com port. Thats it. If possible a multi platform solution is preferred, if not, a MAC program is ok.