CGI

Tips
At the server side, Common Gateway Interface (CGI) is a universe standard to expand Web pages' functions to the programs. But it is slow, cumbersome, and stateless protocol, server frameworks. Thus, APIs are introduced by different companies, e.g. Server Side Includes, ISAPI/NSAPI, Java servlets, Active Server Pages (ASP) and Java Server Pages (JSP), FrontPage Extensions and other dialects.

Most CGI programs are written in Perl and C, and they are free to use.

Useful Web Sites
Bravenet Web Services (more interesting things you will find.)
CGI Rescource Index (you just can not miss it.)

Examples
Tripod site is supporting some CGI programs.