DarkMultiplayer is a mod created by Christopher Andrews for Kerbal Space Program that implements a multiplayer server and client. The server CPU and RAM demands are low enough that a cheap hosting service or home computer can run a number of server instances.
A 20-player stock-parts public server runs on this machine using port 6702. Download the latest client and updater from the link above or via d-mp.org. Once installed, you can use the add server button to create a connection to greenoctagon.co.uk.
DMP allows players to upload screenshots for other players to view in-client. I made a small Ruby script that captures new images, converts them to JPEG and makes them available here.
A full list of public servers on this machine and many others is available on the public server list maintained by VITAS at d-mp.org.