The extension applications are actually just "starter" executables (in Unix they are shell scripts) that invoke either MzScheme or MrEd with the correct arguments. The directory structure is simple, in the main PLT directory the main thing is the "collects" subdirectiry that contains the Scheme application sources, and a "doc" directory in "collects" it that contains some documentations.
When you install the system, you will have an option to create ".zo" files. These files are "compiled" files that can be loaded faster so generally you would want to create them. This step is actually required, since these files have no macros left in them, so if you don't create them, you might have problems because Swindle overrides some of MzScheme's built-in macros. The reason that I have put "compiled" in quotes is that this is actually byte-compiled files, it is an internal binary format that MzScheme uses so the same files are used on all platforms (like Java class files).
From here on, the Swindle home page is where you got this file from. In any case, this page can be found at http://www.cs.cornell.edu/eli/Swindle/.
Then use the installation instruction that you will find there to install DrScheme. When the installation program asks you, you have tosay that you do want to create the ".zo" files, under MacOS you will have to run the "Setup PLT" program yourself to do this.
Notes for Macintosh installation here.
This will unpack Swindle, compile it and create small executables that will run it - "Swindle" is a console-mode version and "DrSwindle" is the full GUI environment.
If you run into any kind of problems, an alternative is to get zipped version and unpack its contents in the "collects" subdirectory - this contains the sources and the byte-compiled files. This, however, means that you'll have to run the setup program again to get the applications starters.
Note: these files always contain the most current Swindle version so you can use them whenever you have any problems.
ln -s /usr/local/lib/plt/bin/* /usr/local/binAlso, remember to `rehash' so the shell will know about these immediately.
Updates are being made automatically, when you run Swindle, use Auto-Update from the Language menu, and the system will be updated as necessary. This must be done when the machine is connected to the Internet. After an update has been performed, you will be asked to restart Swindle.
If anything happens and the system is left in an unstable state, simply reload the plt or zip file again (as said above).