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).
YourPay is a PHP class that can be used to submit WorldPay transactions through a WorldPay account without the very impersonal payment pages provided by the said company. This class will submit the user's credit card details in real-time and return either "Authorise" or "Decline" according to the response.
isbnsearch provides a simple method for retrieving information about any book using only an ISBN or EAN barcode. It is intended to provide assistance for online libraries, user groups, or individual users, and is designed in such a way to provide a distributed ISBN database query system. Users can choose to view the summary information (author, title, publisher, date, edition, subject, ISBN) as HTML, XML, or a pre-formatted SQL statement.