At the beginning would be good to say, that I am writing about mobile apps, not about solutions like SXM, Navtex etc.
Since 2012 when I started regularly sail on the sea, I used many apps and I can see the area is improving quite significantly. Here I am having four links to the best ones.
Navionics - this one I start using for sailing maps. The weather forecast has improved in last versions, but it is not the ideal one. For inshore cruising it could be enough, but the user experience of the app is not ideal.
It takes too long to get to the weather screen, see the tides etc. Navionics is the best for maps definitely better then Garmin, in my opinion.
Predict wind - There is new feature of weather routing. This is handy tool which chooses the ideal route for your boat. It is good to consider the recommendation, but at the end the decision is still on you and you will have to trust your intuition. The weather forecast graphics are definitely better they it used to be. The big advantage is, when you pay for subscription of this app, you can order Iridium Go.
Predict wind is as a native app. https://www.predictwind.com/iridium-go/
Windfinder - This app I liked for knowing the conditions when being in marina or on a shore. It is simple and clear to understand. Also have to say, that it was always quite precise. But sailing according this app I cannot imagine.
Windy - This app is currently my favourite. I like the amount of information, the way the forecasting model is displayed and the accuracy of the forecast was always correct. Guys were asking for some crowdfunding on Indiegogo and got 124% of what they asked for. That also speaks about well done product.