The psychrometric chart is a graph of the properties (temperature, relative humidity, etc.) of air. It is used to determine how these properties vary as the amount of moisture (water vapor) in the air changes. (wikipedia)
A psychrometric chart presents physical and thermal properties of moist air in a graphical form. Usually it requires patient to read it and not get lost with the different axis. PChartz does it for you, just move the mouse and see how the different properties change values (Enthalphy, Dry Bulb Temperature, Wet Bulb Temperature, Moisture Content, Dew Point and Relative Humidity )
pchartz is a beta freeware tool. This program doesn't need to be installed.
PChartz.zip contains the executable file (PChartz.exe). Just unzip anywhere, and double click to run it.