To quote the developers from Berkeley Systems, Inc.
"After Dark is a screen saving shell. It provides all of the support and tools a programmer needs to quickly create unique screen saving graphics"
To be able to use an AfterDark module you must have purchased a full version of one of the AfterDark screensavers.
After
Dark will run on Win95, Win98 and Win ME. Only Afterdark 4.0 modules
will run under Windows 2000 and Win XP due to a compatability issues with
calling 16bit DLLs. You will have great difficulty even getting AfterDark to
install on WinNT.
I appear to have deduced a reliable technique for Installing After Dark on Windows XP which has been tested by several people now.
Versions 3 and below will run on Windows for Workgroups.
If you know of other places to buy Afterdark, please drop me an email.
Amazon sometimes sell second hand copies of this software.
Lucky Mac users can now get Afterdark X for their machines from Infinisys

If you have a 3.0 version of AD for Windows then you can upgrade to 3.2. This is compatible with 95/95/ME.
If you have a 4.0 version of AD for MAC then you can upgrade to 4.04 compatible with Mac O/S 7.1 to 8.0 but not O/S X, for that you will need After Dark X (see above).
A wide range of After Dark Modules have been produced for MAC and Windows.
You can only develop screensaver modules for After Dark 3.0, however these can also be run under the After Dark 4.0 engine.