Harvest is a system to collect information and make it searchable using a Web interface. It can collect information using HTTP, FTP, NNTP, and local files. Supported formats include HTML, DVI, PS, fulltext, mail, man pages, news, troff, WordPerfect, C sources, and many more. Adding support for new formats is easy due to Harvest's modular design.
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.
ZAP! is a module which makes it fairly straightforward to build WWW-based user interfaces for groups of Z39.50-based information resources. It hides much of the complexity of the underlying protocol and requires mostly an understanding of HTML and some understanding of the Z39.50 database model.
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).
METAMOD is a portal solution providing Discovery, Access and Retrieve functionality for scientific datasets along with tools for DAR metadata like automatic extraction, manual editing, and conversion between different formats. Metadata can be converted to different formats and exposed using different search interfaces, i.e. ISO23950 and OAI-PM. It has been designed to be easily integratable with OpENDAP or FTP data servers, and allows data to be uploaded through FTP and HTTP interfaces. A WMS client is built in for visualizing the data.