Epoptes (Επόπτης - a Greek word for overseer) 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!
It can be installed in Ubuntu, Debian and openSUSE based labs that may contain any combination of the following: LTSP servers, thin and fat clients, standalone (non-LTSP) servers or workstations, FreeRDP or X2Go clients etc. It has been translated into more than 40 languages and it's being used in many installations all around the world.
Epoptes website: https://epoptes.org