HyperCard was an application from Apple for their Macintosh computers. The first version was published in 1987. Many people saw it as a quite unique and innovative product, and it was popular for many years. You can find more about HyperCard here. There are still products available today that are in a way direct descendants of HyperCard, e.g. Revolution for Windows, Linux and Mac OS X.
MoStacks certainly is no HyperCard "clone", but is heavily influenced by it and has quite a number of common features, first and foremost of course cards with fields arranged into stacks. MoStacks' programming/script language currently is a lot less powerful than HyperCard's counterpart HyperTalk, but very similar.
20 years ago, HyperCard enabled a lot of Mac users to do something that before was solidly out of reach except for a small minority: writing a Mac application. It would be a big success if MoStacks could do something similar for today's smartphone users: enable them to "program" their smartphones for the first time.