Your phone already runs your life. It might as well run your submission calendar, because the alternative is the graveyard of spreadsheets and sticky notes that currently passes for your system.
Here's the download guide, minus the fake rankings. A mobile app for academic submission deadlines should do five things. Track conference submission deadlines by month. Fire alerts with lead times you control. Sync with your real calendar. Filter by your discipline, so you're not wading through irrelevant CFPs. And work offline, for the conference basement with no signal. If an app does all five, download it. The brand doesn't matter.
The real question is which shape to get. A conference deadline tracker app on iOS and Android? A lab deadline dashboard SaaS with a mobile view? Or just your calendar app with reminders? Honest answer: it depends on how many deadlines you juggle. One or two a year, your calendar is fine, set three reminders each. Five to ten, get the dedicated app. Running a lab where students forget things professionally, get the dashboard and make the mobile app the price of admission to your group.
Add a paper submission checklist app to the same phone. The free ones are fine. Deadline apps get you to the portal. Checklist apps get you through the portal. Different problems, both worth the home screen space.
Whatever you download, remember the division of labor. The app is the alarm, not the calendar. Keep the actual academic conference deadline tracker calendar at confjournal.fyi bookmarked, with dates, locations, and submission links, and let the phone do what phones do best: nag you.
And when the paper is ready, confjournal.fyi will get it submission-ready with paper formatting and submission checks for your target venue.