DaisyDisk - DaisyDisk is a disk analyzer tool for OS X that visualizes hard disk usage and allows to free up hard disk space.
DiskWarrior - DiskWarrior, the world's most advanced and highest rated hard disk, hard drive, and disk repair and data recovery tool for macOS, OS X and Mac OS X.
CleanMyMac X - Clean, protect and speed up your Mac
Data Rescue - When Apple's system recovery fails, recover any and all files with Data Rescue 3. This data rescue software will even work if your Mac's hard drive fails to mount.
MacFly Pro - Smart assistant for better Mac performance
MiniTool Power Data Recovery - MiniTool Power Data Recovery is a freemium data recovery tool that works quite well considering the basic version is the only free aspect of the app.