I've got the PC version of 'Navigate' (http://www.wizworldservices.co.uk/navigate) but it also runs on Macs. I don't know if it works with BSB or grib files (whatever they are).
Well, I think its pretty good as it seems to have everything to help someone navigating (e.g. tides, tidal streams, ocean currents, astro, magnatic variation, leeway). It will do passage planning, connect to a GPS and the coast outlines are free (big bonus for me as I commercial "soft" charts seem very expensive).
There's a trial version that you can download and try.