OpenCPN is a powerful open-source (free to the user) navigation program that has many features of top of the line commercial programs. Downloads and detailed documentation are at www.opencpn.org. There is a Mac and PC version, as well as Linux. It shows both raster navigational charts (RNC), which are graphic images of the paper charts, as well as electronic navigational charts (ENC), which are vector products that include extended navigation information and offer many user display options. We cover ENC usage in our new book Introduction to Electronic Chart Navigation.
OpenCPN is also unique in offering one of the truest presentations of vector chart (ENC) symbols as specified in the IHO standard S-52. This is a complex system, and many navigation programs have either taken shortcuts to simplify the presentation, or they willfully decided they have better ways to present certain symbols that are more useful to the mariner, and they use those, rather than the ones specified in S-52. Some of the diversions from the S-52 standard are minor and do not matter much. Others can be distracting, and hinder the use of ENC charts.
We see numerous examples of this in several nav programs, but as noted this is extremely rare in OpenCPN, which is very good with the S-52 standard of presentation. The one exception I note now has to do with the presentation of minor lights… and I must add immediately that they are aware of this, and it will be fixed shortly, at which time this note will be deleted. But since we use this fine program in our navigation courses, we point this out for now.