Meld helps you compare files, directories, and version-controlled projects. It provides two- and three-way comparisons of both files and directories and supports many popular version control systems.
WinMerge is an open-source differencing and merging tool for Windows. WinMerge can compare both folders and files, presenting differences in a visual text format that is easy to understand and handle.
TestDisk is an open-source data recovery utility that helps users recover lost partitions or repair corrupted filesystems. TestDisk can collect detailed information about a corrupted drive, which can then be sent to a technician for further analysis.
Disk Inventory X
Disk Inventory X is a disk space analyzer utility for Mac OS. It shows the sizes of files and folders in a special graphical way called treemaps.
GrandPerspective is a small utility application for macOS that graphically shows the disk usage within a file system. It can help you to manage your disk, as you can easily spot which files and folders take up the most space.
WinDirStat (Windows Directory Statistics) is a disk usage statistics viewer and cleanup tool for Windows. On start-up, WinDirStat reads the whole directory tree once and then presents it in three useful views.
Converseen is a free cross-platform batch image processor for Windows and Linux that allows you to convert, resize, rotate, and flip an infinite number of images with a mouse click.