Just installed xfreerdp as I found that it provided a better experience when connecting to the Oracle Virtualbox RDP server. Also installed Remmina a tsclient style app with multi-protocol support but discovered no support for RDP connections as installed.

yum install xfreerdp
yum install remmina

Click Tools ==> Plugins in Remmina and you can see the absense of VNC/RDP plugins

The Fix:

Doh install the plugin packages...

yum install remmina-plugins-rdp.x86_64
yum install remmina-plugins-vnc.x86_64

When you launch remmina from the command line you should see:

Remmina plugin RDP (type=Protocol) registered.
Remmina plugin RDPF (type=File) registered.
Remmina plugin RDPS (type=Preference) registered.
Remmina plugin VNC (type=Protocol) registered.
Remmina plugin VNCI (type=Protocol) registered.
Remmina plugin SFTP (type=Protocol) registered.
Remmina plugin SSH (type=Protocol) registered.