The paper at hand discusses the design and implementation of the “Open eCard App”, which is a lightweight and open eID client, which integrates major international standards. It supports strong authentication and electronic signatures with numerous common electronic identity cards in desktop as well as mobile environments. The Open eCard App is designed to be as lightweight, usable and modular as possible to support a variety of popular platforms including Android for example. It will be distributed under a suitable open source license and hence may provide an interesting alternative to existing eID clients.