"The freeware can be started from the context menu of a folder or drive and shows you the size of this folder, including its subfolders in an Explorer-like fashion. Large folders can be identified at a glance thanks to the gradient bar displayed in the background. All scan results can be drilled down to file level and filters, e.g. for files of a certain type, can be applied. TreeSize Free will even scan smartphones and mobile devices."

"SpaceMonger is a tool for keeping track of the free space on your computer. Each file or folder on a given drive is displayed in a box in the main window whose size is a relative comparison to all the other files in your system."

"Incredibly simple meters that live in the Windows 7, 8 and 10 task bar.Three applications are included: One that shows CPU utilization, another that shows memory and the third shows disk IO."

a plugin driven, modern notification system for Gnome

"Visual Directory Explorer is a tool that I wrote to help me clean up my hard drive. It presents a pie chart (or optionally, a bar chart) where each slice is a subdirectory on your computer. Clicking a slice in the pie chart brings up a pie chart of that subdirectory, allowing you to recurse. I use it to figure out which programs are taking up too much space, so I know what to get rid of!"

Search for image dupes and ask to delete it or not.