WinSCP is described by its author as
WinSCP is an open source free SFTP client and FTP client for Windows. Legacy SCP protocol is also supported. Its main function is safe copying of files between a local and a remote computer.
It is a very robust and feature rich FTP client that supports secure file transfer using SSH over FTP. It has many of the usual and expected features like integration into Windows for such operations as drag and drop and insertion into the Send To context menu. Additionally in can be used via the command line to perform many actions available in its GUI such as synchronizing files between remote and local folders or simply uploading files. Many remote commands are also available by right clicking files in the remote pane, such as duplication, move, Tar, Touch, Grep and of course changing file permissions. It is possible to store sessions or login details and even remember last used local and remote directories.
Two perhaps trivial but stand out features are an internal text editor to work on remote files and the ability to actually view such formats as .htaccess files in the remote pane therefore eliminating the risk of overwriting such files that Windows does not recognize, one thing that is really missing on most FTP clients.
WinSCP should run on any system running Windows 95 or later and is currently at v4.1.8. In my experience I have had less problems with WinSCP when compared to the highly rated FileZilla.