The original Megaload bootloader for Atmel ATmega chips was written by, and is maintained by Sylvain Bissonnette. It is described on his site at http://www.microsyl.com/megaload/megaload.html .
I have converted the firmware for CodeVisionAVR use.
At the moment it is just converted for writing to flash. For that purpose it is compatible with Sylvain's windows program.