- The xTalk interpreter archive - Lots of HyperTalk-like programming languages, with source code
- OpenXION - A cross-platform HyperTalk-like programming language written in Java, with source code.
- stackimport - A command-line tool that exports HyperCard stacks into image files and XML suitable for import into other applications.
- Stacksmith - Another open source project intending to create a new HyperCard.
- Pantechnicon - Lots of HyperCard stacks. These are the files that used to be hosted at the HyperCard Pantechnicon. I'm still sifting through these, so not all files have been uploaded yet, and currently it's only a directory listing.
- hypercard.de - German web site with a large archive of stacks
- The xTalk Interviews - Short FAQ-style interviews with various people from the history of HyperCard and its clones.
- HyperCard File Format - A description of the general structure of a HyperCard stack on disk.
- AddColor Resource Format - A description of the general structure of the resources used by HyperCard 2.3 and later to store color information.
- ColdCoffee HyperTalk to Java converter - A bunch of Java source code files that read a subset of HyperTalk and create Java source code from that.
- XFromApp XCMD engine - Old C/C++ source code for running HyperCard plugins (XCMDs and XFCNs). Mostly of historical interest.
- CompileIt! Manual - This is a PDF of the manual to CompileIt!, a HyperCard stack that allows you to write HyperCard command plug-ins that access the Mac's system API and let you do everything any Mac programmer could do.
Commercial HyperCard clones
- SuperCard - The first HyperCard clone. For Mac OS X.
- LiveCode - Originally known as MetaCard, this cross-platform IDE runs on Windows, Mac OS X, Linux, Android, iOS and as a browser plugin.
- BayCard - A modern HyperCard-like system for the Mac with Button Tasks/ClickScript-style programming.