I'm a huge fan of Garmin Pilot. AFAIK there aren't any other apps out there besides hiring a dispatch service that gives you an extra layer of legal protection from things like accidentally filing an illegal alternate or filing without putting an alternate when one is required. There have been times where for example, changing my departure time by 10 minutes is the difference between legally needing an alternate and not. And if you need an alternate, you have to go searching for alternates, then read all their non standard alternate mins, see if they apply, then read the notams, see if those apply, etc. It's easy to accidentally file an illegal alternate, but the app will let me know if the alternate i'm trying to file is allowed or not. FF does not do this. I like that it keeps me legal when filing.