Do you have a product which can shutdown up to 8 PC (Windows + Linux) over Network if temperature is too high in the server room?

There are a couple of ways of achieving this. Probably the best solution is to use the AKCP securityProbe5E. This is an environment monitor which has a sophisticated alert notification and actions including automatic server shutdown. Therefore, you could set this up so that it would automatically shut down PCs over the network should the temperature rise above a set threshold. The other way of doing this is to use the Remote Power Switch IP9258-DS, this has 8 power outlets. The only disadvantage is that it would be a switch-off of power rather than a controlled shutdown.