Some useful websites, apps and tips. Suggestions welcome, send them to hendrik [at] modestine.org.

About the destination

Wikitravel is the wikipedia for and by travelers. 3000+ destinations. Sometimes extended with a lot of practical information. If necessary, switch to a different language to find a more complete article.
Wikitravel in English
Wikitravel in German
Wikitravel in French
Wikitravel in Dutch

How to get there

Overland and by ferry
The Train Line offers timetables and prices from 200 train and bus companies throughout Europe. Buy tickets with credit card or online payment method. Price forecasts and price comparisons. Info about airport transfers. In some cases one ticket for train and ferry.
Trainline in English
Trainline in German
Trainline in French
Trainline in Dutch

Flixbus: more than 2000 bus connections, choose language at the top right
Omio (formerly GoEuro): tickets for buses, trains and flights, choose language at the top right
Aferry: many ferry connections in Europe, 1000 worldwide, online booking in dozens of languages
BlaBlaCar (link to .fr site, choose your language at the bottom right): car sharing in dozens countries.

Flights

Skyscanner: choose your language at the very bottom; alerts service by email
Google Flights: choose your language below; alerts service by email
Flight Connections: airports and the flight connections between them, visualized on an interactive world map

Understand the local language

Google Translate: web service and app for Android and iOS. Dozens of languages. With the app you take a photo (for example from a menu) and you will see the translation. Interestingly, you can use the app offline, which works with dozens of languages.

Exchange rates

Oanda: all currencies, 9 languages, web, Android and iOS

Shortly before your departure

Scan important documents and mail them to yourself. In the event of loss or theft, that can make a big difference.