Windows utility CCleaner ("Crap Cleaner") removes unused files on your PC so it runs faster with more hard drive space.
CCleaner scans your system and identifies Internet Explorer cookies, browsing history, system log files and temporary files for deletion. After analyzing my system (which I thought was pretty clean), CCleaner said it could remove 991.8 megabytes, which is a LOT of disk space. CCleaner also analyzes the Windows registry integrity and can uninstall unused applications as well. CCleaner is freeware, Windows only.
Update: Reader Mandy says, "I downloaded, installed and ran CC Cleaner. It rendered Firefox unusable. It completely distorted the appearance of all graphics among other things. Had to delete CC Cleaner, uninstall and reinstall Firefox and run system restore before things got back to normal." Be sure to backup things before you use CCleaner, everyone. Thanks (and sorry!) Mandy!
Update 2: A reader says, "I've been using CCleaner for months. It does have an issue with Firefox: It doesn't seem to clean the cache properly, even if Firefox is closed. Fixing shouldnt require an uninstall: You can fix it by going to Tools, Options. Then Privacy. Then hit the Clear Cache button." Thanks, Gambit!
Update 3: Tom says, "I tried CCleaner this morning, and I had a different Firefox issue than the ones described earlier: certain URLs would become unreachable. Yet they worked in IE6. Uninstalling and reinstalling Firefox was the only fix; half-way measures such as just reinstalling Firefox didn't do it. As a result, I'll have to pass on CCleaner for now."
Update 4: Mike says, "In CCleaner, in the "cleaner settings" box there is a tab for "applications" and mozilla/firefox is listed there (first, on my home computer) and if you uncheck all the firefox boxes, nothing happens to ugly firefox when all the temp files are swept away elsewhere (I figured this out after I had to reinstall firefox the first time I used it)."