MetaKit is an embeddable database which runs on Unix, Windows,
Macintosh, and other platforms.  It lets you build applications which
store their data efficiently, in a portable way, and which will not need a
complex runtime installation.  In terms of the data model, MetaKit takes
the middle ground between RDBMS, OODBMS, and flat-file databases - yet it
is quite different from each of them.