LibTMCG is a C++ library for creating secure and fair online card games. The library provides a sort of useful classes, algorithms, and high-level protocols to support an application programmer in writing such software. The most remarkable feature is the absence of a trusted third party (TTP), i.e. neither a central game server nor trusted hardware components are necessary. Thus, with the present library there is no need for an independent referee, because the applied protocols provide a basic level of confidentiality and fairness by itself. Consequently, the library is well-suited for peer-to-peer (P2P) environments where no TTP is available. Of course, we cannot avoid that malicious players share information about their private cards, but the protocols ensure that the shuffle of the deck is performed randomly (presumed that at least one player is honest) and thus the cards will be distributed uniformly among the players. Further, no coalition can learn the private cards of a player against his will (except for trivial conclusions). The corresponding cryptographic problem, actually called Mental Poker, has been studied since 1979 (Shamir, Rivest, and Adleman) by many authors. LibTMCG provides the first practical implementation of such protocols. WWW: https://www.nongnu.org/libtmcg/