Metakit is an efficient embedded database library with a small footprint. It fills the gap between flat-file, relational, object-oriented, and tree-structured databases, supporting relational joins, serialization, nested structures, and instant schema evolution. Data files are portable, use auto-sizing ints and strings, and have the ability to very efficiently store binary data, from single bits to multi-Mb objects. The library has been used on Unix, Windows, Macintosh, VMS, and others, spanning a range of 16- to 64-bit architectures, from PDA to S390. The “Mk4py” Python binding is by Gordon McMillan.