In this book we present the design and implementation of KEMS, a multi-strategy theorem prover based on the KE tableau inference system. A multi-strategy theorem prover is a theorem prover where we can vary the strategy without modifying the core of the implementation. Besides being multi-strategy, KEMS is capable of proving theorems in three logical systems: classical propositional logic, mbC and mCi. Some of the contributions of this work are (i) an analytic, correct and complete KE system for mbC; (ii) a correct and complete KE system for mCi; (iii) a multi-strategy prover with the following characteristics: accepts problems in three logical systems: classical propositional logic, mbC and mCi; has 6 implemented strategies for classical propositional logic, 2 for mbC and 2 for mCi; has 13 sorters to be used alongside with the strategies; implements simplification rules of classical propositional logic; provides a proof viewer with a graphical user interface; it is open source and available on the internet at https://github.com/adolfont/KEMS; benchmark results obtained by KEMS comparing its classical propositional logic strategies with several problem families.