FirstClass® Client FirstClass® enables you to experience the power of reliable communication, collaboration, conferencing, and calendaring capabilities in one easy-to-use solution.     The FirstClass® Client software provides a desktop application that is optimized for fast, streamlined access to the FirstClass® server. Choose the version you want to install. Mac OS X(10.4.11 or lower) or Windows or Linux or Mac OS X(10.5 or higher)