How to open the Electronic nautical chart S-57 data?

If your question is simply about viewing the S57 files (extension .000), then you will be happy that GDAL supports that format for reading files. As a result any software using GDAL, like Qgis, can open S57 files. See here for documentation on the S-57 ENC file format. Also see here for a very nice Opensource navigation software.

If you want to write to S57, I do not think that is possible with FOSSoftware yet. Maybe we will have one by the time S100 is released.

There is a free add-on from ESRI to view S57 files.

http://www.esri.com/software/arcgis/extensions/esri-s57