LiveCode Community Edition Overview | RunRev. Yep, it's out. GPL3 version of LiveCode. And yes, all target systems are included - OSX, Windows, Linux, Android and iOS. And they've streamlined it too, the DMG is significantly smaller than the one from the last release (ok, many of the missing things are things that belong to the commercial parts, but still). And it really looks nice, sure, the language is wild, but hey, it's a much better GUI Builder than anything currently delivered with Android tools.
hypercard
OpenXION. For the sake of completeness: an open-source implementation of an xTalk language (the family to which HyperTalk - the language of HyperCard - belongs) in Java. You could, for example, incorporate it into your own projects as a scripting language.
uliwitness/Stacksmith. And since we're talking about HyperCard again - Stacksmith wants to build a clone for OSX. Although I wonder why they exactly follow the (pure black-and-white) original in the graphical representation.
NovoCard. Wow, I've been waiting for something like this for a long time. Unfortunately, it's not for Android yet, but for the iPad, but it could revive my old iPad for a while - a Hypercard clone for iOS that comes with a scripting language based on JavaScript in this case. Everything onboard on the iPad, making it ideal for tinkering on the go. And in general, I think the Hypercard structure fits tablet computers pretty brilliantly. I'll probably play around with it.
I didn't know HyperNext Studio at all. A HyperCard clone for Mac, with which you can also create Windows applications. However, the last version is a bit older, I don't know if it still runs with Lion. Meanwhile, it is freeware (though closed source, I guess because their last version is already a bit older). And also interesting: it offers two languages, one that is modeled after HyperTalk and RBScript, an object-oriented Basic from Realbasic (another IDE for OSX and Windows). I guess HyperNext itself might be programmed with Realbasic. Oh, and with the HyperNext Android Creator you can also build Android applications with HyperNext. The Android Creator is however paid (but not really expensive with 60 dollars). And unfortunately, it is only available for Windows, not for the Mac. Update: those who have Lion can forget about playing with HyperNext Studio, because it is PowerPC code, and there is no Rosetta in Lion. So the maximum OSX version is Snow Leopard.
SuperCard on Lion. And since I just wrote about HyperCard, its spiritual successor - SuperCard - still exists and has been made fit for Lion again. But it's still a Carbon application, so its days are probably counted (or it will become increasingly difficult to integrate SuperCard into current developments if a switch to Cocoa does not take place). And I'm still tempted to buy it, even if it's just for nostalgia. The hacking feeling of HyperCard I only experienced again later in Smalltalk environments (and they are unfortunately also rather dead under OSX).