Windows: If you're constantly being asked to fixed the computers of friends and family you might as well have a few tools to make the process take up less of your time. The free Helge's Switchblade toolkit is a collection of networking, security, system and other miscellaneous portable applications.
You can run the collection from a USB drive or CD-ROM and takes up around 200MB, which makes it easy to have on hand when loved ones ask for impromptu repairs.
In addition to standard tools such as Revo Uninstaller, PuTTY, FileZilla, PeaZip, Malwarebytes Anti-Malware, CClearner, the K-Lite Codec pack and Notepad++ you can also use the program to retrieve and store log files, backup and restore common drivers and run common network commands like ipconfig without having to leave the tool for a command prompt.
All in all this is a seriously hefty collection of tools for the Windows power user. If you fit that description you should give Helge's Switchblade a look.