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
It costs $40. I have no connection with the company - just found it and started using it a month ago and am very impressed.
EDIT: I was assuming you were looking for a tablet/phone app.