Simply the most capable rapid application development tool I've ever worked with, and I've worked just about all of 'em. Probably the fastest interpreter of any 4GL, with a rich and flexible object model, and easy-to-learn HyperTalk-based scripting language. The development environment shows its UNIX roots, which may be an initial turn-off to folks accustomed to ToolBook or HyperCard, but once you learn it you'll be able to do far more than you can with any other cross-platform tool.