Get System Information

How can I get system information like Free/Total RAM memory, Disks sizes, etc?
In windows I can use WMI, but there is a way to do it with MONO running on linux?

If not, maybe I can get this info by executing a "FREE" and "DF" (executing those on command line gives the free memory and disks sizes)... but then how can I get the result from a command line application on my MONO app?

Thanks, and sorry for my bad english :/