Open Source Embedded Data Base library. It fills the gap between flat-file, relational, object-oriented, and tree-structured databases, supporting relational joins, serialization, nested structures, and instant schema evolution.
There's a Python binding for MetaKit.
There's no full-text Search Engine for MetaKit, but Paul Snively thinks it shouldn't be too hard to add.
There's a library on top of MetaKit called [E4Graph] that implements storage for graph-structured data (a superset of tree-structured)
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