Automated formal verification using model checking is a mature field with many tools available. We summarize the recent trends in the design and architecture of model checking tools. An important design goal of modern model checkers is to support many input languages (front-end) and many verification strategies (back-end), and to allow arbitrary combinations of them. This widens the applicability of new verification algorithms, avoids duplicate implementation of the analysis techniques, improves quality of the tools, and eases use of verification for a newly introduced high-level specification, such as a domain specific language.