PUTTY:

This utility is used to connect to remote linux or unix machines, it provides CLI ( Command Line Interface ) to the remote machine. Once putty is opened , type the Hostname and port( port not mandatory, default port is taken )  in the respective text fields and click open , then it will ask for credentials to connect. Putty can be used to do SSH, Telnet and other operations.

Downloadable Link: https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html

Installable : putty.exe ( Release 0.70 )

VNC ( Virtual Network Computing )

This utility is also used to connect to the remote linux or unix machines, It provides GUI ( Graphic User interface ) to the remote machine. Open VNC  and then go to File→ New Connection and then provide the remote HostName to connect, Once you click on host name icon, it will ask for the credentials to connect.

Downloadable Link: https://www.realvnc.com/en/connect/download/vnc/

Installable : VNC-Viewer-6.17.731-Windows.exe

MSTSC ( Microsoft Terminal Services )

This Utility is used for connecting to the remote windows machines. This utility is provided by default in windows machine, you can go to run and type mstsc, then a dialog box will be popped up , which will ask for the remote host name along with credentials, once you enter the required details , remote windows desktop will be opened in a new window. This tool provides GUI.