Expedia Germany, Austria and Switzerland operates as a regional hub of the larger Expedia network, but with a notably tighter focus on what matters to people in those three countries. The site handles flights, hotels, and flight-plus-hotel combinations, with real effort put into showcasing deals for obvious destinations like Italy, the Netherlands, Berlin, and New York. You're looking at the same booking engine Expedia uses globally, which is both reassuring (it works) and occasionally frustrating (it's built for volume, not finesse).
The appeal here is straightforward. Prices are quoted in EUR or CHF depending on where you're browsing from, and the deals themselves are regional. That August sale or the "Kleine Preise" (small prices) promotion you'll see advertised actually reflects what's happening in that market at that moment. Most people using this site are planning holidays within Europe, though transatlantic flights to New York crop up regularly in the current deals.
It's not fancy or particularly innovative as travel sites go. The interface is functional, sometimes clunky. But if you're sitting in Zurich or Vienna or Berlin and want to quickly cross-reference flight and hotel prices without wrestling with currency conversions, it's the obvious choice.