Another really interesting freeware chart program that I've been playing with lately is "CapCode". It may not be for everyone but it's a wonderful, powerful program for data geeks like me.
Written in Java so it runs on just about anything.
Incoporates oodles of NMEA 0183 data, GRIB data, AIS, wind, all kinds of stuff.
Really, really great boat speed polar calculation/display functions.
It has a GPS simulator program so you can figure the program out at home first.
It's sort of "modular" so you can run lots of it or just the parts you find interesting.
Documentation is minimal to non-existant, you're pretty much on your own. Fortunately most of it works fine right out of the box, though you have to be willing to spend some time experimenting to set it up and to figure it out. If you don't enjoy this sort of thing it's going to seem closer to "user hostile" than "user friendly."
It truely is a beta program and the development of it seems to have slowed down or maybe stalled.