Net::Z3950::SimpleServer is a Perl module which implements the server side of the Z39.50 (information retrieval) protocol. It hides the complexity of network exchanges, packet serialization, and session handling. You are required only to implement simple callbacks to support searching and record retrieval. It is the basis of the "Zoogle" project, which is a Z39.50 gateway to the Google web index.
OpenIsis provides a library and tools to access CDS/ISIS databases, which are mostly used for bibliographic data (ISO2709, Z39.50) but also well suited for other catalogues due to the very flexible indexing mechanism. Based on a C library, there are also bindings for Perl and Java (Tcl to come).
UnixODBC.pm provides Perl programs with a subset of the X/Open ODBC API for use with EasySoft's unixODBC DBMS libraries, as well as a peer to peer API for querying ODBC data sources on networked systems. In addition, it provides peer client and server scripts and configuration files, sample clients that perform ODBC queries on local and networked systems, result set output for RSS feeds, and two multi-host data managers: one that uses Apache and CGI to provide a Web browser interface, and another that uses Perl/Tk.
Berkeley DB XML is a native XML database engine for use within your product. Made available as a C++ library with language bindings for Java, Perl, Python, PHP, and Tcl, it integrates directly into your application (it is not a standalone database server). It provides XQuery access into a database of document containers. XML documents are stored and indexed in their native format using Berkeley DB as the transactional database engine.
Triceps is an innovative embeddable Complex Event Processing (CEP) system. It can be thought of as an in-memory database driven by triggers, or a data-flow machine working on a stream of events, or a spreadsheet on steroids. The major architectural advantages of Triceps include the direct use of procedural logic (as opposed to all-SQL systems), support of both compiled and general scripting languages (C++, Perl), light weight, and easy extensibility.