I have been using SEAiq and it is fantastic. You can use CM93 and BSB/KAP
charts with it, as well as other charting formats. You can even make your own
charts and use them. If you have an
internet connection, you can pull down
Google Earth images for any region you are navigating in. It also connects
NMEA data via
wifi, if you have that capability, and handles
AIS data well.
It costs $40. I have no connection with the company - just found it and started using it a month ago and am very impressed.
Mark
EDIT: I was assuming you were looking for a tablet/phone app.