TechTool Deluxe was a part of the AppleCare Protection Plan. It is based on Micromat's powerful TechTool Pro diagnostic and repair utility. TechTool Deluxe checks the major computer components covered under the AppleCare Protection Plan.
This review was originally posted on VersionTracker.com. I had a problem with my iMac G5 (hung on a black screen before fully starting up). Ran Apple Hardware Test, which reported no problem. Than I ran TechTool Deluxe. It ran for 7 hours, when I accidentally found a report on the web which makes it abundantly clear that TT screws up your machine when you use it with Tiger.