Not quite sure where you want to go? No problem. Kiwi lets you search "everywhere" as a destination, showing you deals from, well, everywhere. As a bonus, this app has the Kiwi NOMAD feature, where you can search multidestination trips. One of the cooler highlights of Kiwi is the baggage calculator (of sorts). A point of your phone's camera in the app will help to determine whether your luggage might pass through without extra fees or if you should take out that extra pair of shoes.
Note: the Kiwi app is only available for iOS users.