These are few FTP opensource software for windows and Mac.

Windows

1. File Zilla  -  Downoload

Features

Among others, the features of FileZilla include the following:

• Easy to use
• Supports FTP, FTP over SSL/TLS (FTPS) and SSH File Transfer Protocol (SFTP)
• Cross-platform. Runs on Windows, Linux, *BSD, Mac OS X and more
• IPv6 support
• Available in many languages
• Supports resume and transfer of large files >4GB
• Powerful Site Manager and transfer queue
• Bookmarks
• Drag & drop support
• Configurable transfer speed limits
• Filename filters
• Directory comparison
• Network configuration wizard
• Remote file editing
• Keep-alive
• HTTP/1.1, SOCKS5 and FTP-Proxy support
• Logging to file
• Synchronized directory browsing
• Remote file search

For Mac

They work in both modes FTP / SFTP

1. Cyberduck - Very good all-around ftp program.
   Download Page
2. OneButton FTP - Simple, fast FTP, with a focus on “advanced queuing”.
   Download Page
3. Fugu – Not as polished as Cyberduck (and only for SFTP) but has a side by side interface showing your files and the remote files. Download Page