Maptech has a free viewer version of their product:
Free Boating Charts
The link to the free software is at the bottom of the page.
It seems pretty full featured to me, but I'm a noob. I've been playing with the software for a while now and plan to use it to select and define waypoints to load in my old aviation
GPS, then use in conjuction with paper
charts on the boat.
Not the most elegant, but the price is right and I don't really need a
chartplotter at this point in my sailing evolution anyway.