BleepingComputer Review:

NTREGOPT, or NT Registry Optimizer, is a Windows Registry defragmentation utility.  Over time as entries are added and deleted from the Windows Registry, gaps are created. These gaps are unused space that takes up unnecessary disk space and reduces the overall performance of accessing the Registry.  NTREGOPT rebuilds the Registry so that it is compact and does not contain any extra spaces.

To be safe, before you use any tool that modifies the Windows Registry, please back it up using ERUNT.  This allows you to restore your Registry in the event that there is an issue.

This program is offered as two downloads. The main download is a installer version that will install NTREGOPT onto your computer for you.  The ZIP version does not include an installer and allows you to place the NTREGOPT files where you wish.  Regardless of the version you use, please read the README.TXT for more information on how to use the program.

Product Description from Lars Hederer:

Similar to Windows 9x/Me, the registry files in an NT-based system can become fragmented over time, occupying more space on your hard disk than necessary and decreasing overall performance. You should use the NTREGOPT utility regularly, but especially after installing or uninstalling a program, to minimize the size of the registry files and optimize registry access.

The program works by recreating each registry hive "from scratch", thus removing any slack space that may be left from previously modified or deleted keys.

Note that the program does NOT change the contents of the registry in any way, nor does it physically defrag the registry files on the drive (as the PageDefrag program from SysInternals does). The optimization done by NTREGOPT is simply compacting the registry hives to the minimum size possible.