The program on your ecu that runs your engine is called a rom. It is either a .bin or .hex file.
Everything is explained in detail on Getting Started. Please read it.
Monochrome has taken the stock rom from the 1999 3000GT VR4 and disassembled it. Basically he reverse engineered the program.
After he accomplished this feat he then started adding extra functions in the rom. He called his new rom Chrome.
The latest version is Chrome V2.0.
ECUFlash is available for download via Tactrix.com and is a computer program that can read the rom with a definition file Monochrome created. You can then change the values you need to tune your car. EcuFlash also allows you to flash the custom rom to your Flash Ecu.
Evoscan is another computer program that can talk to your Flash Ecu and datalog information off it. This information can be use to determine how to tune your car. Monochrome also had to create a definition file for this program to datalog the 3S Flash Ecus.