GNU AIS is software for demodulating and decoding Automatic Identification System messages used by ships to navigate. You will need a VHF receiver with discriminator output to get it to work.
Use map data to plan hikes or explore new areas. Includes 3D maps of terrain rendered in real-time; trace trails across the terrain and get height verses distance profiles; tile together adjacent maps to create seamless map areas. Reads USGS SDTS files.