Air Explorer is probably the most similar tool to FTPie you'll find. They're both desktop applications for Windows, both use a dual-pane file manager layout, both support FTP and cloud storage, and both let you drag files between different services. If you put screenshots side by side, you'd see the resemblance immediately.
But the similarities are more surface-level than they first appear. The two tools have different priorities, different pricing models, and different ideas about how much a file manager should do. Let's dig into the actual differences.