Mac: Previously mentioned iBoostUp, the powerful system cleanup utility, is 50 per cent off today only. While we initially reviewed the free version, you can get the $10.49 premium version for only $5.49.
While the free version does a good job of cleaning your system, iBoostUp's premium offering does a more thorough job. It can clear out your memory, find duplicate files, remove unnecessary code from your apps that make them take up extra disk space, locate files you aren't using and much more. You can get these options through the free version through in-app purchases, but iBoostUp Premium automatically includes everything now and in the future. This way you won't have to pay for upgrades you want as time goes on. A couple of in-app purchases add up to $5 anyway, so you might as well just get them all. Discount or not, it's a heck of a lot cheaper than competitor CleanMyMac.
iBoostUp Premium ($5.49) [Mac App Store]