The original software was written for Microsoft Windows, but now there are also versions that run on Linux and Unix. The tool also includes a file transfer facility, which can be made secure by adding in SCP and SFTP. The basic program has no security, but you can combine it with SSH to add on authentication and encryption to protect remote connections across the internet.
It enables you to log into another computer, which may be on the same network, or that could be accessed over the internet.