We've been writing some open source software:

Tkrzw: a set of implementations of DBM
Tkrzw-RPC: RPC interface of Tkrzw
Kyoto Cabinet: a straightforward implementation of DBM
Kyoto Tycoon: a handy cache/storage server
Tokyo Cabinet: a modern implementation of DBM
Tokyo Tyrant: network interface of Tokyo Cabinet
Tokyo Dystopia: a full-text search system
Tokyo Promenade: a content management system
Hyper Estraier: a full-text search system for communities
Estraier: a personal full-text search system
QDBM: Quick Database Manager
Jakuzure: Simple Photo Album Tools
Tkrzw-Dict: English-Japanese Dictionary