From the project’s github page: Czkawka is a simple, fast and free app to remove unnecessary files from your computer.
This is an excellent, fast tool for finding duplicates, large files, etc.
I was running out on my home directory and freeing up lots of space with this tool turned out to be super easy.
Baobab is good too for the more manual process of finding the largest files/folders
I like ncdu
Is there some hidden feature to find duplicates in ncdu??
I use jdupes for that