Cyberduck is always one of our favourite free FTP utilities on both Windows and Mac, but if you have no need for a GUI and would prefer a command line utility, Duck will do the job.
iOS: Transmit is our favourite FTP app for the Mac, and now it’s available on iOS. It sports pretty much the same feature set as the Mac app, and with deep iOS 8 integration, you can upload files from just about anywhere.
There are lots of great Raspberry Pi projects you can make. Add to the growing list using the small computer as an FTP server — a solar-powered one, no less.