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I'm sure there's lots, but it also depends on your definition of success. Here in Chicago we've got groupon, threadless, braintree, thinkorswim, 37 signals, orbitz, and then, of course, a number of places which have cashed out to acquisitions (like feedburner).

Wooga, Soundcloud, Spreadshirt and maybe Amen come to mind (all Berlin based). Not to name the hugely successful Samwer clones like Zalando (biggest online shoe e-commerce business in Europe, Zappos clone).

Skype was started in Europe