Cyberduck - A libre FTP, SFTP, WebDAV, S3, Backblaze B2, Azure & OpenStack Swift browser.
FileZilla - FileZilla is an FTP, or file transfer protocol, client. It lets individuals transfer single files or batches to a web server. For many years, FTP was the standard for website design. Read more about FileZilla.
ProjectSend - ProjectSend is a self-hosted application that lets users upload files and assign them to specific clients.
WinSCP - WinSCP is an open source free SFTP client and FTP client for Windows.
Transmit - Transmit is an FTP client for Mac OS X and Mac OS Classic (which is unsupported).
Forklift - The most advanced dual pane file manager and file transfer client for macOS.