Many years ago, there was HyperCard, included free with the Macintosh in the late 1980s. It got a lot of attention because it was one of the first tools that made it trivial to create GUI applications. Apple couldn't figure out how to properly market or position it, so it eventually died of apathy. RunRev has been publishing Revolution, now named LiveCode, as a spiritual successor to Hypercard, for a while, and LiveCode now shares one more important trait with Hypercard: It's now free. See all software downloads.
LiveCode Community Edition is the free, open-source, implementation of LiveCode. It has virtually all the features of the commercial edition, with one major exception: All apps created with it must be open-source. This means that it cannot be used to create apps for Apple's App Store (as the license is not compatible). While it's possible to create and distribute commercial programs with LiveCode Community edition, the open source nature will work against most business plans.
LiveCode applications are based on the concepts of "stacks," with each stack containing one or more "cards," and each card containing a mix of shared items (such as background images and fields) and unique items (such as text in a field, or a control which appears on only one card. An application can have many stacks, and this is often how dialog boxes and special windows are implemented: A stack holds one card, which is the dialog.
The entire development and editing environment for LiveCode is written in LiveCode. That's something you could never do with HyperCard or its older clones and siblings. LiveCode might not be what you want to write the next Word or WoW in, but it's an excellent tool for custom applications, especially many kinds of utilities, vertical market programs, and internal corporate tools. It's also an excellent teaching tool... mostly.
The major drawback to LiveCode Community Edition is that although it has many new and cool features, such as a powerful data grid that can embed complex forms in each cell, the documentation hasn't kept up with the program. The nicely indexed and organized reference dictionary is several iterations behind the code base. The multi-hundred page PDF manual is clear, well-written, and also several versions old. There are plenty of samples and walkthroughs on the LiveCode site, but you've got to dig around to find them. There's a "LiveCode Academy" that has detailed lessons and tutorials.... but most cost money.
RunRev is actively working to fill in the gaps in the documentation, and asking users to contribute, but be prepared to do a bit of digital legwork to find all of the information you might need to use any of the newer features.
A second, minor, bug is some interface oddities. Some dialogs float and some don't, some of the tools do not work exactly as specified (sometimes due to the documentation being for the Mac version), and so on. Nothing critical, but you'll need to get used to LiveCode's quirks.
I began my professional programming career with HyperCard. I am very happy to see a version that's very 21st-century aware, with decent database and Web functionality. Now that the price has dropped to "free," I strongly recommend at least looking over LiveCode and seeing if it's a useful tool for you. See all software downloads.