What are some alternatives?
When comparing TreeSize and WPMU DEV, you can also consider the following products
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
Gravity Forms - Gravity Forms is one of the best and easiest contact form plugins to create modern forms for websites powered by widely-used WordPress.
WizTree - WizTree quickly finds the files and folders using the most space on your hard drive. It scans the MFT (Master File Table) instead of crawling the entire disk which makes it very fast.
Yoast Plugins - Yoast offers plugins to improve SEO and optimize web sites and blogs.
SpaceSniffer - SpaceSniffer is a freeWare (donations are welcome) and portable tool application that lets you understand how folders and files are structured on your disks.
Pareto Security - Pareto Security is a Wordpress Security plugin