As of January 8, 2015 OpenCPN version 4.0.0 is available as a stable release.
OpenCPN, the go to PC or MAC software for cruisers sailing both on and off the beaten tack.
Charts for most USA waters can be found here: http://www.nauticalcharts.noaa.gov/mcd/enc/download_agreement.htm
Charts of the ENTIRE world are a litte harder to aquire, just walk the docks and ask a salty looking cruiser for a copy of their CM93 v2 charts. Note: USE CM93's with caution as not everywhere is accurately charted (i.e. Tonga, Fiji, Vanuatu and many other remote locations). No fault of the charts, it's just the accuracy of the underlying survey of some very old surveys on which the charts are based.
Supplement and compare the above charts with super accurate Google earth images that you can custom create using GE2KAP found here: http://www.gdayii.ca/
OpenCPN is a great planning tool, that can also be used for live navigation, weather analysis and much more.
That's it for now.