Perhaps ways to color code countries - and have communiy moddable color codes. This way I can share a list of countries where certain things are illegal to have on board and share that list, or where
provisioning might be easier. This could even by by island or area rather than country per se.
Basic functionality without
internet to include things like NOAA
charts and basic routes.
Compass bearings along a planned
route with a way to enter in DMS or DM.XX and get out a
compass bearing to carry on.
Tidal currents would be great... but short of that having the tidal tables for planning bar crossing or figuring when you want to shoot along a straight with the tide.
There is a ton that goes into it. I am probably not the best person to weigh in here as my experience is primarily with local cruising. I am not sure how expansive you want this app to be. If you can calculate which way would be the best to sail from point A to point B while avoiding the bad spots in between that would be great. Including a time - and perhaps taking the polars of a
boat and currents into account? A way to build polars up by logging points of sail and speed would be great too.
I have a very long wish list, I also have some suggestions I wouldn’t part with for free unless this is going to be open source.