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You can pick one of several apps track what time your flight or maybe a colleague or customer's flight will be arriving.
This personal finance app lets you keep track of your expenses, organize your personal income, and plan your budget. It lets you build charts and graphs, warn you of upcoming bills, and track your credit card usage.
Price: $3.99 but there is a free stripped down version.
This app is one of many public transportation apps that are geared to the specific city that you are visiting. It works offline and tracks the Chicago Transit Authority and bus schedules including as the app calls them, the night owls.