What is it? 

Active Local Pages (ALP) is an extensible engine capable to run special modules called content generators. Through them ALP incorporates ability to execute ASP pages, CGI scripts and other WEB application types.

ALP does not depend on Personal WEB server or Internet Information Server. It uses its own modules to serve similar functionality but without need of network or WEB server installed on the machine.

How?

ALP registers and handles its own protocol name - alp:// (also called namespace) and can be invoked from any URL that begins with such namespace specification. Thus ALP is handler of the requests made through this protocol but instead of downloading a resource from the network it processes the request locally on the client machine.

And it runs in the Internet Explorer?

Yes. In the Internet Explorer you can type ALP URL and this will invoke the engine. Depending on the what  the URL points ALP will process it as ASP page, as CGI script and so on - depending on its configuration.