With Spotify, you can listen to the artist, album or playlist of your choice for free in shuffle mode. To listen to the title of your choice or download music to listen to it offline, you must upgrade to premium.

Facebook Messenger is the app to install to use the Facebook chat function on your mobile. In addition to chat, it offers the same features as SnapChat.

Duolingo makes learning foreign languages fun.

Maps.me is an app that uses data collected by OpenStreetMap to create maps that are available offline. OpenStreetMap data is crowdsourced, like that of Wikipedia.

Skype allows you to make free calls over the Internet, with or without video, to another phone that has the app or to a computer connected to the software.

Linguee is a dictionary that allows you to translate many languages offline.

XE Currency allows you to convert all currencies in the world. This app is very useful for planning your budget, doing your accounts and avoiding being scammed when changing your money.

Airbnb works a bit on the same principle as CouchSurfing, except that it costs money. Individuals offer to rent a room in their home or their entire home when they are away.

WhatsApp allows you to send messages or call your loved ones. You can also send and receive photos, videos and voice messages.

Convenient for translating texts in more than 70 languages without an Internet connection.

Google now covers almost the entire planet. It is possible to download part of the map to your phone to be able to access it offline:

Although most of the time you find accommodation once you arrive there, Tripadvisor is very useful for finding reviews. You can also note the places you have passed to help other travelers.