Deskreen turns any device with a web browser into a secondary screen for your computer.
RustDesk
Yet another remote desktop software, written in Rust. Works out of the box, no configuration required. You have full control of your data, with no concerns about security.
Gnome Connections
A remote desktop client for the GNOME desktop environment
KRDC
KRDC is a client application that allows you to view or even control the desktop session on another machine that is running a compatible server. VNC and RDP is supported.
Vinagre
Vinagre is a remote desktop viewer for GNOME.
Remmina
Use other desktops remotely, from a tiny screen or large monitors.