Epoptes is an open source computer lab management and monitoring tool. It allows for screen broadcasting and monitoring, remote command execution, message sending, imposing restrictions like screen locking or sound muting the clients and much more!

Possibilities:
✔ view client monitor images;
✔ remote control and execution of commands;
✔ demonstration of the server image on client computers;
✔ sending messages to the client(s);
✔ group client management (shutdown or reboot);
✔ remotely setting restrictions, for example: locking the screen or muting clients;
✔ work both in LTSP installation and without LTSP.

and much more!