Remmina

Remmina is a remote-desktop client written in GTK, to
use other desktops remotely, from a tiny screen or large monitors.

Remmina supports multiple network protocols in an integrated and
consistent user interface. The protocols currently supported are:
X2Go, RDP (Remote Desktop Protocol), VNC (Virtual Network Computing),
and SSH (Secure Shell / Open SSH).

External plugins are also supported to add new protocols and features.