What are /r/travelhackers' favorite Products & Services?

From 3.5 billion Reddit comments

You list of app is very informative. Kwikpay app also has the potential to be one of the best travel mobile app. It gives you freedom to top up your prepaid mobile (iOS/android) anytime, anywhere & any operator. Next time you don't have to look for top up vouchers in shops when you travel.( https://play.google.com/store/apps/details?id=com.uk.recharge.kwikpay&hl=en ) (https://itunes.apple.com/in/app/kwikpay-mobile-top-up/id990590563?mt=8 )