Sometimes we might download some files with extension name .nrg, which is a kind of CD image file created by Nero, usually we can open it with a variety of software, such as burning tool - Nero ImageDrive (under Nero); Virtual CD ROM - DaemonTools or Alcohol 120%, as well as UltraISO. But some software can only open .iso file, does not know .nrg format file at all, so nrg2iso will be of use now.