Rapid environment editor - Rapid Environment Editor - freeware Windows environment variables editor
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
eveditor - Your trusty environment variables editor
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.
Path Editor (Open Source) - Edit PATH environment on Windows conveniently.
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.