cgi-util is a fast, easy to use C library for creating CGI programs. Functions are available for initialization (parsing), grabbing fields (by string, integer, double or boolean value), embedding HTML files, and more. It accepts both POST and GET request methods and has extensive error handling.
Ilib is an image manipulation library for developers. It's capable of reading and writing images (PPM/PGM, PNG, JPEG, GIF, XPM, BMP) and many drawing functions including drawing lines and text using any BDF (X11) font. It's great for generating GIFs/PNGs from a CGI or generating graphs. Ilib includes sample applications for generating graphs for HTTP access.log files and QuakeWorld server frag log files and a tool for creating image indices from a group of images.
Sablotron is an XML toolkit which implements XSLT, DOM, and XPath. Sablotron is written in C++, and it can be used from C, Perl, Python, PHP, ObjectPascal, and via a command line interface. It supports the XSLT 1.0, XPath 1.0, and DOM Level 2 W3C specifications. It is designed to be as compact and portable as possible, and is maintained as an Open Source project by Ginger Alliance.
Websuite is a suite of simple CGI programs written in C, designed for speed, high availability, and support of name-based virtual hosts. The programs are designed such that in the event of failure they cannot affect the web service, and are designed to use a powerful debugging API which can give systems operators detailed notification of any problems. They include features such as a server-side clock, random billboard, email gateway, and error handling scripts and daemon. They are designed primarily for the Apache-1.3 web servers and have not been tested on any other.
php_template is a very fast and easy to use PHP template rendering system. It can create large amounts of data quickly, given a simple template. It supports dynamic data tags for things like table data and lists, optional tags for conditional data presentation, and simple variable tags.