wRASP (Rocket Altitude Simulation Program for Windows) is free rocketry simulation software that calculates velocity and altitude. It is based on the origional RASP written in BASIC by Harry Stine.
wRASP, unlike RockSim, does not allow the user to design the rocket. The user must supply the correct diameter, weight, and drag coeficcent in order to get accurate results. It can simulate any rocket on any motor in its database, simulating velocity and altitude until apogee or recovery system deployment. It can give deployment speed, but does not calculate decent rate.
wRASP is a 16 bit program, and runs on Windows 3.1 through Windows XP. (Vista untested).