BoardingBuddy
Checks you in for flights on major airlines right at the 24-hour mark and sends you your boarding pass.
Problem
It's easy to forget the 24-hour check-in window, which can mean a worse seat or boarding group and a scramble at the airport.
Solution
It checks you in automatically on major airlines as soon as check-in opens, sends back your boarding pass, and keeps a log so each confirmation is only checked in once.