iTALC is a free, open source, computer management system. It enables teachers to control student computers, including monitoring what the students are doing, remote control to help users, lock out workstations, send text messages to students, remote power on/off and reboot and more.
It is extremely easy to install and use. It took me less than 10 minutes to download and install the admin version on my computer. I loaded the software and the key onto my network drive and then logged on to each computer in my room (there are 8) and installed the client version in less than 3 min for each computer. It then took a few minutes to set up the main system on my computer with all the classroom computers linked.
iTALC is similar to systems like LANSchool, but free.
The wiki is also very helpful with the installation and set up.