kyotocabinet (straightforward implementation of DBM)

Kyoto Cabinet is a library of routines for managing a database.
The database is a simple data file containing records, each is a
pair of a key and a value. Every key and value is serial bytes with
variable length. Both binary data and character string can be used
as a key and a value. Each key must be unique within a database.
There is neither concept of data tables nor data types.
Records are organized in hash table or B+ tree.