Stacksocial offers Prosoft Engineering Drive Genius 4 for Mac for $49.99. (The software is sent via instant digital redemption.) That's the lowest total price we could find by $49. The software creates a bootable secondary drive, measures drive performance, repairs errors, checks for corruption, alerts you to problems, and purports to optimize and speed up your Mac. Deal ends August 5.

Update: As a reader discovered, Other World Computing offers it for $49.