Good news for owners of Android smartphones and tablets: the MX Mariner GPS chartplotter app is now available in beta. This looks like a great live-navigation app for all boaters with GPS-enabled Android devices. For only $5.99, using free charts, the app offers a wealth of features and likely has more expensive competitors cringing. MX Mariner comes from the same folks who developed the free OpenCPN chartplotting software for laptops - a terrific program developed by sailors and chock-full of great functions.