OpenCPN is an Open Source Chart Plotter.

Full Sail has an instance of OpenCPN running on a RaspberryPi 3 ($30) coupled to an BU-353S4 USB interfaced GPS puck ( $30) and a GeChi 15.6” screen ($200) and a 16GB microSD card ($9).
The addition of a Bluetooth keyboard mouse combo ($17) brought the entire plotter to completion.
There is a quite lively forum covering OpenCPN theĀ  Cruisers forum and the project can be found at opencpn.org

I have found the system to be an outstanding tool, although I have a smaller Garmin chart plotter the OpenCPN system greatly exceeds the Garmin and has easily enabled my limited sailing skills to take me out into the Big Boy areas of the Chesapeake Bay and return as it I were following a Google Map route.