This article is from the alt-sources-mac FAQ, by Mark Pilgrim (firstname.lastname@example.org) with numerous contributions by others.
Source code can be for the entire Macintosh line (including the Centris and
Quadra lines), Newton, and the new PowerMac line of Macintosh computers.
Source code can be for any Macintosh operating system (6, 7, 7Pro, etc.), as
well as Bento, A/UX (as long as the source is A/UX specific and does not apply
to UN*X in general), etc.