QModMaster is a free, Qt-based Modbus master application. A graphical user interface provides easy communication with Modbus RTU and TCP slaves, and a built-in bus monitor lets you examine all traffic on the bus.
QModMaster is based on libmodbus for protocol communication and QsLog for logging. It supports both Windows and Linux. For Windows, a pre-compiled binary is available — no installation required, just unzip and run.