PuTTY is a free, open source client for remote access to protocols like SSH, Telnet, rlogin.
It provides connection to a remote host, a server, for example, and manages it.
It includes several utility software such as PuTTYgen that is used for generating SSH-keys, SCP client and SFTP client used for file copying, etc.
Originally the tool was elaborated for Windows platforms, now it is supported by Linux platforms as well.