Free Client Software
SSH
An SSH client gives you command-line access to a Linux server.
Windows: PuTTY
Mac: SSH is already built in. Just open a Terminal window and type "ssh" to use it.
VNC Viewer
A VNC viewer allows you to access your remote desktop on a Linux server.
Windows: RealVNC Viewer for Windows
Mac: RealVNC Viewer for Mac
WARNING: Do not install "VNC Server". The "VNC Viewer" is all you need.