Its primary feature was its ability to express build patterns in an imperative language which supported structured namespaces (similar to Pascal records) and simple lists.
[1] FT Jam is a popular variant maintained by The FreeType Project and is fully backward compatible, although its features are being integrated into Perforce Jam.
The Boost C++ Libraries is using a Jam variant called "Boost.Jam" (or "BJam").
Unlike with makefiles, the writer of the Jamfile need not manage these dependencies, only list the source code files themselves.
There are some packages such as AutoJam designed to solve some of the problems of Jambase.