System

CCleaner

http://www.piriform.com/ccleaner

Cleans cache, registry, temporary files, etc ... Maintains system performance on the long term.

Bleachbit

http://bleachbit.sourceforge.net/

Cleans unnecessary files from the system. Optimizes the configuration of Mozilla Firefox and Thunderbird.

Defraggler

http://www.piriform.com/defraggler

Defragment hard drives.

Recuva

http://www.piriform.com/recuva

Recovers deleted files. Ineffective if the hard disk is damaged, but very usefull for the recovery of deleted files.

Zero Assumption Recovery

http://z-a-recovery.com/

File recovery tool able to recover data from NTFS partition whose MFT is corrupt.

This software is not freeware.

R-Studio

http://www.r-studio.com/

Data recovery tool able to deeply scan a hard drive to find files based on their MIME signatures.

This software is not freeware.

Xpy & Vispa

http://xpy.whyeye.org/

Disable identification features built into Microsoft Windows XP, Vista and 7. Protects privacy.

Thanks

• Thanks to Jean (Bad Wolf) for pointing to R-Studio in the comments.