DAEMON Tools is an advanced application for Microsoft Windows which provides one of the best optical media emulation in the industry. DAEMON Tools enables you to use your CD/DVD images as if they were already burned to CD/DVD.
This is the best app for opening iso or nrg files, or in fact any kind of disc image. The one provided is the latest version of the small software.
It doesn't slow down your PC at all and is the best of its kind. Also no crack or serial required as it is free for everyone to use.
I think this is better for normal use than the Pro version because of similar functions and much lesser memory footprint.