The fast, stable, and always free Linux RDP client

One of Remmina’s many features is a RDP client in the connection manager with many tunable options to get you connected just how you want

Remote Desktop Protocol - Wikipedia

Remote Desktop Protocol (RDP) is a proprietary protocol developed by Microsoft which provides a user with a graphical interface to connect to another computer over a network connection.[1] The user employs RDP client software for this purpose, while the other computer must run RDP server software.