HF Propagation Prediction and Ionospheric Communications Analysis
Free professional HF propagation prediction software from NTIA/ITS, originally developed for Voice of America (VOA).
This guide should get you well started with VOACAP. A more comprehensive discussion about the finer details of using the software can be found in George Lane's book Signal-to-Noise Predictions Using VOACAP. A User's Guide.
PROPAGATION PLANNER - Professional HF contest & DX expedition planning tool
VOACAP ONLINE - Professional-grade high-frequency (3-30 MHz) point-to-point propagation predictions
VOACAP ONLINE COVERAGE MAPS - Professional-grade high-frequency (3-30 MHz) coverage area predictions