HDB is a small, flexible, and efficient hybrid database, a mix between a filesystem and a database. It comes with a wide range of command line utilities for manipulating and extracting data. It's designed for both embedded and bigger systems. It currently has interfaces to C, C++, Java, and Perl.
HDBC provides an abstraction layer between Haskell programs and SQL relational databases. This lets you write database code once, in Haskell, and have it work with any number of backend SQL databases (MySQL, Oracle, PostgreSQL, ODBC-compliant databases, etc.) HDBC is modeled loosely on Perl's DBI interface, though it has also been influenced by Python's DB-API v2, JDBC in Java, and HSQL in Haskell.
HeliDB is a database for storing key-value pairs from a Java program. The client program creates one database object per database file. The database objects can be configured to support different capabilities. In its simplest configuration, a database is a file-backed map. More advanced configurations can give it transaction support or fast record searches by indexing records in a B+ tree.
Hybrid HTTP API Tester is a general purpose API tester GUI. You can specify a URL and send GET or POST requests to it as a client with an interface allowing you to set up a database of API commands and their parameters. It is useful for probing 3rd party APIs or building your own.
IRC-API is a stateful, asynchronous IRC API written in Java. It offers an (a)synchronous programming model to its user, and has the ability to save the IRC server state per IRC connection. It supports SSL. The API has been tested on various IRC networks, including EFnet, DALnet, and Undernet. It offers a useful, detailed interface to the Server it connects to.
IdealMySQL is a PHP class that provides an interface for working with MySQL databases. It can connect to a database, execute queries on a database, check variable names for validity, and catch errors and email them to the administrator. All error messages are stored in a text file that can be easily edited, and the look and feel of the error output to the user is controlled by a style sheet.