qtVlm is a navigation software designed for real and/or virtual sailing boats. It is also a free weather grib viewer that accepts most of the existing gribs. It can read and display maps in various formats, such as georeferenced charts (kaps, geotif, geojpeg, etc.) and mbtiles files.It includes an AIS module and an Instruments Module, that can retrieve data from various NMEA sources, or from internal GPS.Rasters and mbtiles maps are added by simply putting them in the relevant qtVlm directory, or via the import/export module.qtVlm can be used simultaneously in two modes:In real boat mode, qtVlm will show the boat's position and calculate the best course using Route and Weather Routing modules. Many options are available, like multi-routing to find the best departure date-time according to various parameters, or taking in account segments with engine, etc. qtVlm can acquire position and NMEA information via various sources (internal GPS, tcp, udp or gpsd), and can display many navigation instruments.In virtual mode, once registered to one of the numerous races organized by Virtual Loup de Mer (VLM: http://v-l-m.org), qtVlm connects to VLM server to control the boat, to set the autopilot or to calculate the best course using route and routing modules, etc. Whether you are a real sailor or not, it's the best way to learn weather routing science and techniques.Geo-referenced marine maps (kap, geotif, geojpg, etc.) can be loaded, and weather faxes can be displayed over the map. qtVlm can also display maps from Tiles Servers, or from mbtiles files.Several grib files can be loaded at the same time, in order to be able to route using various parameters (winds, currents and waves for instance).Route and Weather Routing modules, navigation instruments, anchor alarm, mbtiles and AIS modules are available only with the full version, available through in-app purchase. The full version also add automatic rasters quilting.qtVlm is also available freely on PCs (windows, mac/os, linux), including all modules and fonctions.